Impulsivity, simply put, is the tendency to act without thinking.
This type of behavior reflects having little or no forethought, reflection, or consideration of consequences. This trait is common in children; common examples include hitting or kicking as a result of anger or chasing a ball into a street without considering traffic. The tendency towards impulsive behavior reduces with age.
In adults, however, impulsivity sometimes manifests itself in behavior that is self-sabotaging. Examples include behavior that is inappropriate to a situation, plans that are poorly conceived and/or prematurely expressed, and actions that are unduly risky. This can include some types of criminal behavior (shoplifting and petty theft, causing injury or death due to sudden anger), relationship failures (getting involved too seriously or quickly with strangers), or dysfunctional workplace behavior (arguing with superiors, refusing to follow rules and procedures). Extreme impulsivity can be a symptom of some personality disorders including borderline personality disorder and psychopathy.