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We often can't rely on ourselves to act rationally. We know this, but much social science has a bad habit of ignoring it. A more realistic role for rationality is needed to grasp the unhidden but unmodeled relationship between decisions and actions. We evolved to frequently act without deciding. The widely used Rational Actor Model rests on three assumptions: First, life is a stream of decisions, second we make them consciously, often by calculation, and third, they lead us to act rationally. One of many demonstrations that these are all frequently false, is the reliable failure, despite what we consciously and rationally decide, of most self-improvement resolutions. Much of what we do isn't consciously considered or calculated on the spot, and what we know often doesn't cause us to act accordingly. The Rational Actor Model isn't an action model; it's a decision-model that sadly ignores how we do much of what we do. It is fundamentally aspirational, under-empirical, and applies only in limited situations. Yet this "rationalist delusion" still dominates economics. Behavioral Economics--its name amusingly highlighting what's been lacking-- offers hope. Its discoveries, which you and I experience every day, but which un-behavioral economists typically ignore, include "cognitive biases." Daniel Kahneman says these "systematic errors" trace to our "machinery of cognition." This is progress, but it's a near-reaching revolution, another repair to the old rationalist clunker. We can do better. Better behavioral models should be, like us, habit driven. Our lives are often a stream of habitual actions. We repeatedly reap their harvest, on autopilot. We consciously decide only if that flow is interrupted. Thinking is expensive and reinventing cognitive or behavioral wheels is rarely productive, so we evolved to acquire second nature habits from others. As Darwin noted "much of the intelligent work done by man is due to imitation and not to reason." We are habit-formers and habit-farmers. Each habit can be modeled as a situational trigger with an action script. Habits are behavioral tools enabling rapid action without costly conscious attention. In triggering situations, they can be overruled, but only with conscious effort. Action scripts likely use rule of thumb style conditional logic, rather than cognitively unnatural numerical methods. Habits can be rationally useful or irrationally unfit for a given situation. It's worth considering whether cognitive biases are bad cognitive habits--badly triggered action scripts--rather than built-in brain bugs. Especially since what is called rational, requires training. We must be rational when habits are acquired, since later they will be repeated without deliberation. As Aristotle noted living well required "rational habits." Force of habit shapes our lives. Shouldn't it also shape our behavioral science models? Especially those we build institutions on. Bring on the habitology and the habitonomics. Illustration by Julia Suits, The New Yorker Cartoonist & author of The Extraordinary Catalog of Peculiar Inventions. Previously in this series:Kahneman and Bentham's Bucket of HappinessKahneman's Clarity: Using Mysterious Coinage in ScienceWhat Rational Really MeansThe Cognitive Science of Star TrekColonoscopies Clarify Inner Workings of MindsHappiness Should Be A Verb