The more you repeat a behavior, the more you reinforce the identity associated with that behavior. In fact, the word identity was originally derived from the Latin words essentitas, which means being, and identidem, which means repeatedly. Your identity is literally your “repeated beingness.

Habit formation is incredibly useful because the conscious mind is the bottleneck of the brain. It can only pay attention to one problem at a time. As a result, your brain is always working to preserve your conscious attention for whatever task is most essential. Whenever possible, the conscious mind likes to pawn off tasks to the non conscious mind to do automatically. This is precisely what happens when a habit is formed. Habits reduce cognitive load and free up mental capacity, so you can allocate your attention other tasks.

True behavior change is identity change. You might start a habit because of motivation, but the only reason you’ll stick with one is that it becomes part of your identity. Anyone can convince themselves to visit the gym or eat healthy once or twice, but if you don’t shift the belief behind the behavior, then it is hard to stick with long-term changes. Improvements are only temporary until they become part of who you are.

But when we repeat 1 percent errors, day after day, by replicating poor decisions, duplicating tiny mistakes, and rationalizing little excuses, our small choices compound into toxic results. It’s the accumulation of many missteps — a 1 percent decline here and there — that eventually leads to a problem.

Behavior that is incongruent with the self will not last. You may want more money, but if your identity is someone who consumes rather than creates, then you’ll continue to be pulled toward spending rather than earning.

If you want to master a habit, the key is to start with repetition, not perfection. You don’t need to map out every feature of a new habit. You just need to practice it. This is the first takeaway of the 3rd Law: you just need to get your reps in.

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One solution is to avoid making any single aspect of your identity an overwhelming portion of who you are. In the words of investor Paul Graham, “keep your identity small.” The more you let a single belief define you, the less capable you are of adapting when life challenges you. If you tie everything up in being the point guard or the partner at the firm or whatever else, then the loss of that facet of your life will wreck you. If you’re a vegan and then develop a health condition that forces you to change your diet, you’ll have an identity crisis on your hands. When you cling too tightly to one identity, you become brittle. Lose that one thing and you lose yourself.