system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: the birthday paradox. With a group of 23 people why are 2 of them likely to share a birthday?
gpt
In a group of 23 people, you can pick a pair of people in 253 different ways.

So, even though the number of people seems small at first glance, there are actually a lot of chances for a shared birthday.