This document discusses habits, defining them as fixed ways of thinking, feeling, or behaving acquired through repetition of a mental experience. It notes that keystone habits influence the formation of other habits. Habits are reinforced through a habit loop involving cues, routines, and rewards in the brain. While habits can help conserve mental energy, bad habits are undesirable behaviors that can be replaced through recognizing triggers, changing routines, and finding new rewards. The key to changing habits is using the same cues but changing the routine while still providing rewards.