The evil that men do lives after them;The good is oft interred with their bones.
It means that when people do evil acts it has lingering effects, if someone destroys someone's life it affects their children and friends and family. People are scarred from the bad things that happen to them. Whereas when good people do good acts, although it might be helpful at the time, it rarely has long-term effcts, the good that they do ends when their life ends.
It's a pretty pessimistic view and not one I would subscribe to, it's just that when people do really evil acts they do have huge consequences (eg Hitler). To do really really good acts I think you have to be a super-dedicated person or at least rich and have a conscience. Not many of us get the power and influence to do good things that can really change the world.