I dare do all that may become a man;
Who dares do more is none.

Macbeth. ACT I Scene 7.

Also quoted, in Hugo Weaving's mellifluous voice, in V for Vendetta.

Oddly enough, I heard it from both sources within one weekend. It remains stuck in my head.
It comes off better from V, because, of course, very shortly after spouting this bold declaration of manly restraint, our man Macbeth dares all sorts of things that most likely do not become a man.

Sigh.

I'm sure nobody would ever do the WRONG thing if doing the right thing seemed like it would be as much fun.