The streak mechanic — a count of consecutive days you've performed a behaviour — is one of the most powerful tools in digital health and education. Duolingo built an empire on it. NutriBalance uses it to keep people logging food for months instead of days. But why do streaks work? And how do you use them effectively to build lasting health habits? The Psychology of Streaks Streaks exploit several well-documented psychological mechanisms simultaneously. 1. Loss Aversion Daniel Kahneman's Nobel Prize-winning research established that the pain of losing is roughly twice as powerful as the pleasure of equivalent gain. A 30-day streak isn't primarily valuable because of the reward you get for reaching 30 days. It's valuable because breaking it feels genuinely bad — worse than the neutral feeling of never starting the streak in the first place. This asymmetry is why streaks are so effective: once you've built one, the motivation to avoid breaking it significantly outweighs the motivation that started it. 2.…