Habits stick because every repetition casts a vote for an identity, not because of the outcome any single repetition produces.

Writer on habits and decision-making

So one of the core lessons of atomic habits is that every action you take is like a vote for the type of person you wish to become. So, when you show up at the gym today, you are casting a vote for being the type of person who doesn't miss workouts. When you sit down and make one sales call, you are casting a vote for being a salesperson. When you write one sentence, you are casting a vote for being a writer. And no, doing one push-up does not transform your body, but it does cast a vote for that identity.