Those who have nothing to lose, such as the punk on the street. Street fights are brutal and one is wise to avoid it, but if it is unavoidable, one must react full on without reservation with the intent to incapacitate the attacker as they will likely not relent until they are unable to react.
The person with a lot to lose, well if they have enough money they can really make your life miserable. But they play that game on a bigger scale than just you or me, unless we directly oppose that persons actions. Think politics.