Your Design Is Simple And Intuitive

Spent 6 weeks perfecting that "simple and intuitive" fingerprint scanner, only for users to try scanning with their knuckles. No matter how foolproof you think your UI is, someone will always find a way to use it wrong. It's like building a door with a giant "PUSH" sign, and watching people pull it anyway. The gap between designer intention and user reality is where dreams go to die.