S:

Utilitarianism is a theory in normative ethics holding that the proper course of action is the one that maximizes overall "happiness". 

Scenario one: Imagine walking down a dark street. A large man jumps out from behind a bush with a pistol intent on shooting you dead. you grab the gun and strain to keep the barrel from being pointed at you. You can feel that you are loosing the struggle and stab him repetitively with a knife from your pocket. The man drops the gun, falls backwards and dies over the coarse of a minute or so.

Scenario two: Imagine walking down a dark street. A large man jumps out from behind a bush with a pistol intent on shooting you dead. You make no attempt to resist and he shoots you in the head. You die instantly.

In both scenarios a man is killed. However in the first scenario the man killed feels considerably more pain than the victim in the second. Thus it seems a Utilitarian is committed to claiming that if faced with such a situation the proper course of action would be to let yourself be shot in the head. However because the second scenario is superior in moral terms it seems that maximizing happiness is not always the most moral outcome.

S.