If you get 23 people in a room the odds of two of them sharing a birthday are 50%
The birthday paradox is a veridical paradox: it seems wrong at first glance but is, in fact, true. While it may seem surprising that only 23 individuals are required to reach a 50% probability of a shared birthday, this result is made more intuitive by considering that the birthday comparisons will be made between every possible pair of individuals. With 23 individuals, there are (23 × 22)/2 = 253 pairs to consider, far more than half the number of days in a year.