The 5% Rule:

No matter how kind, warm, thoughtful, amazing, cheerful, consistent, and perfect I treated people roughly 5% of them would just be terrible (yes, I have the numbers to back this). I’m not talking about people who were having a bad day or people who were trying to work the system. There was a legit 3% to 5% of people that just wanted to be mean, nasty, selfish brutes. People that were unpleasant to be around. People who for one reason or another “wanted the world to burn” ( in the words of Christopher Nolan).

This mirrors my own experience in virtually every area of life.