Impetuousness is the noun: the quality of doing things too quickly, without careful thought, or a stretch of behaviour that shows that quality. You can speak of someone's impetuousness as a habit of character, not only of one moment. It is a rather bookish word; in ordinary talk people more often say impulsiveness, or just “he rushes into things.” Though actually, writers still like it when they want a slightly older, slightly heavier feel — youth's impetuousness, the impetuousness of first love. Like the adjective, it is not always blame. It can name a kind of heat that also makes people brave. What it does not name is simple speed, or a plan that happens to be fast.

衝動；魯莽（指這種個性或作風）