The Birthday Paradox: Your Intuition Is Wrong
Question: How many people needed in a room for 50% chance two people share a birthday?
Your intuition probably says: 183 people (half of 365 days)
Actual answer: Only 23 people!
With 50 people: 97% chance of shared birthday
Why this matters: Our brains are terrible at probability and randomness. We need mathematical tools (statistical significance) to know when patterns are real vs random noise.
This is why you can't trust your gut about whether test results are meaningful.