Why does the birthday paradox feel so weird? (1 Viewer)

[Ahsoka]

The birthday paradox states that a group of 23 people will have a 50% chance that someone will share the same birthday as another person. To many people, this seems way too low. But why does it feel so off?

A major reason for this is that people subconsciously compare just their birthday to the others. The chance of your birthday lining up with another person is very very small, 1/365 chance. Even with 23 people, your chance of sharing a birthday with someone is only around 6%. But you need to remember that in this paradox, each person doesn’t compare their birthday just to you, just also to every other previous person. So the 23rd person will compare their birthday to 22 other people. With that in mind, it ca start to make more sense why it only takes 23 people to reach a 50% chance of a shared birthday.

 

[Ahsoka]

General taglist:
@athenarose @intothevault @Nyaz @Dreamer_of_Songs @Yachii @Nina @pinkmelodies @velvet @A_Different_Beat @ChuuAntics @AllTimeChiara

 

[Selfmate]

are we saying exact birthdate? like including the year
or only the day and month?

also who shares a birthday with LSM

 

[dark_tranquility]

unless you're a twin : o

 

[Ahsoka]

are we saying exact birthdate? like including the year
or only the day and month?

also who shares a birthday with LSM

Just day and month

 

[Ahsoka]

unless you're a twin : o

That will be an easy loophole

 

[dark_tranquility]

That will be an easy loophole

lucky me then lol

 

[drokis]

You've hit on the core reason: our brains are wired to think egocentrically when it comes to probability. We instinctively frame the question as "What's the chance my birthday matches someone else's?" rather than the far more expansive "What's the chance any two birthdays in this group match?" The sheer number of potential pairings (the combinatorial aspect) grows so rapidly that it quickly overwhelms our linear, one-to-one mental models, leading to that surprising "off" feeling. It's a brilliant illustration of how human intuition often struggles with non-linear growth.

 

[uran]

There's 50% chance I've been in yo mama

 

[ChiaraStar169]

interesting!

 

[Ahsoka]

You've hit on the core reason: our brains are wired to think egocentrically when it comes to probability. We instinctively frame the question as "What's the chance my birthday matches someone else's?" rather than the far more expansive "What's the chance any two birthdays in this group match?" The sheer number of potential pairings (the combinatorial aspect) grows so rapidly that it quickly overwhelms our linear, one-to-one mental models, leading to that surprising "off" feeling. It's a brilliant illustration of how human intuition often struggles with non-linear growth.

And I feel like probability is often taught that way for simplicity, at least at the start when we learn it in school. I don’t think that’s the only reason it happens, I’m sure it also just easier to view it from that perspective. But I imagine it doesn’t help either if that’s how it’s framed when we start learning about it in school.