Habit, in psychology, any regularly repeated behaviour that requires little or no thought and is learned rather than innate. The behaviour becomes more automatic with each repetition. Some habits, however, may form on the basis of a single experience, particularly when emotions are involved. Habitual behaviour is a form of automatic and routine behaviour. It is behaviour that people repeat, because this behaviour is easy, comfortable or rewarding.  Habitual behaviour's automatically character is demonstrated by the fact that it is often started by a cue or a change in the situation. How much of what we do is habitual? Studies by neurobiologists, cognitive psychologists, and others indicate that from 40 to 95 percent of human behavior—how we think, what we say, and our overall actions—falls into the habit category. Most of the time, bad habits are simply a way of dealing with stress and boredom. Everything from biting your nails to overspending on a shopping spree to drinking every weekend to wasting time on the internet can be a simple response to stress and boredom. One popular method to build habits is called the 21/90 rule. The rule is simple enough. Commit to a personal or professional goal for 21 straight days. After three weeks, the pursuit of that goal should have become a habit. Once you've established that habit, you continue to do it for another ninety days.