Science & TechMental model
23 people in a room, and two probably share a birthday.
With just 23 people, the chance that two share a birthday already exceeds 50 %. With 50 people it's 97 %. Intuition fails because you think about yourself: your odds of finding a match are small. But 23 people form 253 pairs, and every pair is a chance for a hit.
Useful: Coincidences are far more common than they feel; always ask how many pairs were possible.
Source: en.wikipedia.org