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From Instinct to Insight - How Do We Really Decide? Bayesian Thinking - Future IQ

6,560 views Wait, is this logic right? • Apr 11, 2025
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Slog Reference: Understanding Bayesian Updating

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Do you really believe in facts? Or are you just believing what you want to believe? In this episode, we talk about something called Bayesian Updating – a fancy way of saying how your brain mixes your past beliefs (priors) with new evidence to make decisions. But here’s the twist: your priors (like what your family, school, or culture told you) can change how you see the evidence!

We use a fun example with an aptitude test and talk about how your bias can sneak in, even if you think you're being smart. Learn why people sometimes ignore good data, how your brain builds beliefs, and why you should always check if your thinking is based on facts or old stories.
This episode connects to lots of cool Future IQ topics like bad decisions, groupthink, preference falsification, and costly signaling. So if you understand this, the rest will make WAY more sense!

More Videos For You:
Believing is Seeing: https://youtu.be/bxx-My8J_kM
You are in a Cult: https://youtu.be/eEfmHpstjSg
Showing Off Is Important: https://youtu.be/0YEBK7eR3Ek
Your Unpopular Opinion Is Popular: https://youtu.be/Pwh90BkWRt8
Why We Make Bad Decisions: https://youtu.be/CBIm7TqXQ4w
Rohit Sharma Lost 12 tosses in a row - Fixed or Coincidence?: https://youtu.be/EY4WCmIJLcY

Hope you enjoyed FutureIQ by Navin Kabra and Shrikant Joshi. Do hit us up on Twitter:
@ngkabra http://twitter.com/ngkabra
@shrikant https://twitter.com/shrikant

Listen it on the podcast provider of your choice: https://tapthe.link/FutureIQRSS

Sources:
https://en.wikipedia.org/wiki/Bayesian_inference : Wikipedia
https://www.youtube.com/watch?v=HZGCoVF3YvM : 3blue1brown on Bayesian Theorem
https://lesswrong.com : community for understanding priors and helping reduce your biases
https://www.lesswrong.com/posts/bJ2haLkcGeLtTWaD5/welcome-to-lesswrong: Intro to LessWrong
https://astralcodexten.substack.com/p/towards-a-bayesian-theory-of-willpower: Theory that willpower can be explained using bayesian updating

00:00 True Future IQ Style
00:11 Are You An Evidence Based Person?
01:49 Evidence Isn't Evidence?!
03:15 Let's Get Deep Into This
05:35 Beliefs & Priors
06:21 How Does Prior Affect Evidence?
08:04 Where Do These Bias Begin?
10:11 Is All Of Life Bayesian Updating?
13:09 In Professional Life?
13:53 In Social Life?
14:13 In Politics?
14:55 Why Is This Important?
16:23 Science Of Incorrect Decisions

#futureiq

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Understanding Bayesian Updating

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Transcript

This episode very few people are going to watch but I hope you do because it's important and it goes to the core of what this channel is about. So I hope you like it and I hope you share it with your friends. Shriant, do you think of yourself as an evidence-based person? Absolutely. When you see some data, even if you don't agree with it, you will believe what it says. 100% always. I'm a very evidence-based person. Most probably not. Okay, let me give you an example. Okay, there are two candidates and they have come for a job and I administer an aptitude test to them.
Okay, one of them does very well and another does badly. Okay, what do you think about these two candidates? The person who did well on the aptitude test is the one who you should get for an interview. Right. Okay. Now if I give you some additional information okay the person who did very badly happens to be a graduate of IIT Bombay top five in class okay now what do you think uh probably a bad day for him probably something didn't work maybe you should give the test again to him now the person who did very well in the test happens to be from a no-name local college and has a bad percentage in four years of engineering
What do you think? Uh I don't want to say it out aloud, but uh you think he's cheating. Well, you said it, not me. You should definitely give that person the test again. The data, which is the aptitude test, your interpretation of it changed based on the college and academic performance. Yeah, but Naven IIITB top five candidate. That is my point. That evidence isn't evidence. It depends on what you believed before the evidence also. Right? This is a concept in statistics called Beijian inferencing. Right? Okay.
What it says is that a decision that you make, a belief that you have doesn't just depend on the evidence you are seeing right now. It depends on what you believed before you saw the evidence. Okay. So fundamentally you start with some belief that oh I Bombay is a good college. All students of IT Bombay are smart. Top five in class is definitely going to be smart. Yeah. Local college students high chance of them being dumb especially if they scored less than 50%. in comparison to the IIT Bombay student I'm saying. So these are your beliefs before you saw any evidence right these are called priors okay and any belief any decision that you make starts with
the priors looks at the evidence combines the priors with the evidence and that's how you reach your decision right so belief is prior belief plus evidence gives you the new belief right okay but wait these priors that you're talking about these are also So accumulation of evidence over time right for example IITB I know that the graduates of ITB are good you yourself are an ITB graduate so we should understand how these priors got built up right this accumulation of evidence that you're talking about there is very specific way in which it happens okay so let's start that right now uh I believe that I Bombay graduates are good yes right and then one of them does well on
the aptitude test my belief strengthens a a little more right and this happens like you know probably has happened 50 times in the last 10 years correct which is why now I believe that I Bombay graduates more or less are good and something similar that people from a local college with bad grades uh end up doing badly right again 50 times it has happened in the past each time that belief gets strengthened correct correct so this is my priors getting strengthened reinforced correct So that new decision also becomes a part of the prior in future decisions. Correct? But the reverse also happens. Right? Now that this one IT Bombay candidate has done badly in the test, there is a
chance that that is going to slightly reduce my prior on IT Bombay candidates right and if this keeps happening then I might end up with some new prior like you know oh since co I Bombay graduates are duds right or there actually is a prior that oh ever since the J became an objective exam the students are not good enough anymore right I've heard this one yes yes so this is how priors get updated I mean you might have a strong prior but if the evidence keeps piling up piling up against it then slowly the prior goes down right ah but these are still evidence- based so I am still an evidence-based person not necessarily
there are different kinds of priors I might call them borrowed prior for example you might get prior from your family and culture like people who drink and smoke are bad people and they're going to waste their life and you better not hang out with them or you might get it from your school like you know following the rules is a good thing getting good marks is the most important thing in life and so on right you might get prior from the media like all celebrity marriages are screwed up right religion is another source of lots of priors right you can just pick your own religion pick your own prior and there are so many examples full of them of
them absolutely a lot of our biases and stereotypes that we have are prior Right. For example, for example, I have this belief that uh someone who speaks fluent English or fluent any language that I can speak is definitely a good person to hang out with. Correct? And all of us have biases. For example, once I went to a software company and I saw a very well-dressed woman with makeup there and I just assumed that she can't be one of the developers there. Right. Okay. But I hope you updated your priors there. Yes. All right. So all of the evidence that we collect over time over life is basically updating the prior to some kind of a right conclusion right
mostly that is true and we hope that is how all of our life works but sometimes there is a problem there right okay because the prior affects how you view the evidence okay wait how what simple example remember we talked about the aptitude test huh and that was evidence yes and Just because of your prior on the college, your complete view of the aptitude test changed. Oh, this person had a bad day. Oh, that person cheated on the test. You see how that works? That evidence is no longer evidence just because of your prior. Yeah. So, in that case, my prior was actually a bias and that affected the evidence. Well, it depends. Okay. Because maybe it is true
that you know aptitude tests are just a bad idea and so you were right and your prior was correct. The evidence is wrong. Okay. But the reverse might also be true which is that you were really biased against local colleges and people with low grades. Right? And as a result you never ever update on the evidence. Okay. Yeah. So in fact this is a very important special case called trapped prior which prevent you from ever seeing any evidence right and you're just stuck. uh we will cover that in the next episode in much more detail. Right? Just to give you a quick example, uh the entire antivax movement essentially is an example of a very strongly trapped
trial because it started with one paper by Andrew Wakefield about how vaccines cause autism. And that one single paper is the one that is cited every time antivaxers want to oppose vaccines. Just one single paper. There are thousands of papers about how vaccines are actually beneficial. None of those get cited. Just this one paper by Wakefield gets cited. Just an example. We'll talk more about it in the other episode. Yeah. But here's a question. Where do these biases begin? Because if I am updating my prior on the basis of evidence, eventually I have to come to the right thing. So biases must begin somewhere, right? Very simple, right? When you were a baby, h where did you get all your beliefs from?
your parents, right? Your parents can't do anything wrong. Why? Because you know you are crying, you have no idea what's going on. Your parent comes, puts something in your mouth, and now you're happy. Amazing. What a genius, right? Again, you are crying, you have no idea what's going on. Your parent comes, cleans your butt, and you're happy. What a different genius, right? So for the first five years everything that your parent says is like you know just God's word. By the time you start realizing that your parents can make mistakes a whole bunch of priors are already set already set. But then you get a whole new set of people to believe, right?
Because your teachers in school are like everything the teacher says is absolutely true and you come home and you tell your parents and your parents try to tell you no no no beta that's not how it works and you're like you know where did this person come from? My teacher said it and obviously that's true, right? Then by the time you are 15 years old, it is your peers, your friends, right? What your friends say and this guy heard so and so and did so and so and now suddenly that's what you believe and in your 20s it is like bosses and YouTube uh creators like us.
Yeah. So all of these like we mentioned earlier these are borrowed priors and those are the source of lot of biases borrowed more like shoved into shoved down our throats prior these are okay but I do see that happening in various aspects of our life even now now that we consider ourselves thinking people and independent and free will and thought and whatnot. See fundamentally all of life is Beijian updating right I mean basically I am sitting here right and you didn't murder me why would I well in the African savana if you just go sit with someone there's a good chance he'll murder you right true kind how do I know you won't murder me I have a prior there
right yes uh and that I'm not worried about getting food in the evening because you know there is going to be a person at home who's cooked food for me. That's a prior. Okay. We don't realize these things. These are so automatic. Most of our world works on prior, right? Yes. But there are a lot of spots in day-to-day life where you can see that you know this is like at the edge of being right versus wrong. Okay. For example, so take movies for example a new Salman Khan movie has come out.
Would you watch it? No. Okay. But if Mita tells you that this is actually a good movie, you should watch. Would you watch it? 100% I would watch. So what has happened is that based on your past experience, you had a prior on Salman Khan movies. Yes. But then based on some other experiences, you had a prior on Mita's reviews about movies. Yes. Right. So and we are constantly updating that. Right. If Mita tells you to watch that movie and it turns out to be bad and then one more Sman movie she makes you watch, you're going to adjust your prior on Mita. Yes. But if you like those two movies, you're going to adjust your
prior on Salman. Yes. Right. Long-term relationships. There's another sequence of Beijian prior. Right. Go on. Say more. She sent him a message. He didn't reply. She's going to assume that he's not interested. Right. takes time to reply. We are literally like struggling with our thoughts. We we are trying to figure out what will not set you off. So give us time. Focus focus the priors here, right? Uh after a few months of this happening, she realizes, oh, it's not that he's not interested, but he has all these issues. Okay. Yeah. These are not issues, man. I mean, you have to be careful with me. Later on, you know, right? He tells her to do something.
Okay. and evening he finds out she hasn't done it. that depending on what prior he has about her can either lead to a full blow up you never care about what I want or oh she might have forgotten maybe busy day today right is she an IT Bombay or local college I mean I don't mean that literally just apply the same concept that the aptitude test she didn't do it depends on the prior right correct yeah actually a lot of uh relationships go through similar kind of problems but how those problems are resolved depends on how the relationship has progressed up to that point. So it is updating in a very strict and straightforward sense. Right?
Professional life is also full of Beijian updates. Right? Your boss tells you to do something at Friday evening 5:00 p.m. Do you have to do it in the next 1 hour or can you go off and do it on Monday morning? This is actually a question for all of you. If your boss asks you to do something on a Friday evening, do you do it in the next hour or do you wait till Monday to do it? And whether whatever your decision is, think about it. It's based on a whole bunch of prior there are probably like five priors the here right please comment and let us know we are very curious because I depending on which boss it was I would
either do it on Friday itself or I would be okay waiting till Monday. In social situation also there's a whole bunch of priors right uh you and Rohan have decided to meet at a restaurant at 7:00 do you go at 7 or do you go at 7:30 depends on what prior you have on Rohan change the name from Rohan to Raa and I will go at 8:00 to meet him for a 7:00 meeting yeah politics politics is full of this stuff right here is a great example from the US okay this is results of actual ual surveys of Republicans and Democrats asking them what they thought how well they thought the economy was doing and you can see that when their
own party president was in power they think economy was doing great and these guys think it was doing badly and then when the president changes it flips over he literally see the point of change coinciding with the change of president you don't need any other information to know that this is not based on data this is based on prior and bias. Absolute data and absolute bias. Wow. We are uh we are so conflicted as a species. We think we are evidence-based but uh we are mostly prior based. It seems yes we have a prior that we are evidence-based but that's a good way to put it. So I think the important thing why is this so
important right? First of all, understand that all your decisions are a combination of priors and evidence, right? And whenever you take a decision, especially important ones, right? If you can separate out the prior from the evidence, just be aware of this, your decision making will improve, right? Second is to know that your priors can become pathological to a point where you start rejecting evidence. Okay? Uh we will talk about this in more detail in another episode, right? And it's mind-blowing. You should watch it. But being aware of this and knowing how to get out of that black hole is important.
It can change your life. You should subscribe so that uh you get notification when that episode drops or actually it might have already dropped. Check. And the third thing is that this is such an important base concept that it shows up in many places, right? A lot of future IQ episodes are based fundamentally on Beijian updating, right? We talked about the science of incorrect decisions. Yeah. Priors, right? In fact, the entire episode now that I think about it can be directly linked to these priors and this concept of Beijian updating because every single thing that those people did in that experiment that we've talked about in the science of incorrect decisions was on the basis of priors. Even though they
thought they were talking about it in terms of evidence, you could clearly see the priors that prompted them to do that. Go check that episode out. Line it up after this. It's not just this episode, right? Everything, right? The episode on group confformance. Yeah, prior. The episode on preference falsification prior. The episode on costly signaling. Why do does costly signaling work even if it is fake? Because we have a whole bunch of priors, right? So your understanding of other future IQ episodes and mental models will improve once you have a good handle on Beijian updating and prior. In fact, what we'll do is we'll create a playlist of all of these videos and make that
available for you to watch in a one in one single sitting. Binge on this content and also subscribe to this content and uh let other people know about the stuff that we are doing because it makes us happy when uh you know other people also uh watch it and we need more of this knowledge to spread in the world and uh let other people also update their priors. Sri Kant Naven Future IQ Bingi