Impulsiveness is the name for acting on a sudden feeling before you stop to think about danger or trouble. It is a noun: not the one act itself, but that way of acting, or that side of a person. A child who grabs the last cake, a shopper who buys a coat they did not plan, a driver who changes lanes with no look — people point to impulsiveness in all of these. Parents and teachers use it in ordinary talk; doctors who study the mind use it in a more careful way, as a pattern that can last. Though actually, it is not the same as being brave, and it is not the same as being quick. A brave person may still think first. A quick person may already know the answer. With impulsiveness, the thinking comes late, or not at all. People also stretch it for small happy things, like an unplanned snack. The core stays the same: a push from inside, and no pause.

衝動；衝動的個性。心理或教科書才說「衝動性」。