Simplicity is key.
Numbers, Music, Coffee, and Purdue History.
Paying attention to lyrics instead of just listening for the deepest buried sound in a song.
You can do anything for a year.
Anybody who effortlessly gets up before 6 am, because it's a time completely to yourself since nobody else can manage to get up at that time.
Saying most words or short phrases backwards almost immediately.
Musician or bikesmith.
Frivolous numbers - old bank account numbers, phone numbers from childhood friends, addresses to somebody's vacation home I've been to once.
The Prisoner's Dilemma from Game Theory Economics.