Leinster's Law

Leinster's Law states that in a typical society, the chances of someone else having exactly the same birthday increases as the number of people in that society grows. When a group reaches about 23 people, there's about a 50% chance that at least two individuals share the same birthday. This counterintuitive idea highlights how, with enough individuals, common attributes like birthdays are more likely to be shared than one might expect, due to the combinatorial nature of comparisons within the group.