I can't think of a better guide to adult behaviour than the beginning of Sam Spade's explanation of why he's going to turn Brigid O'Shaughnessy over to the cops in Dashiell Hammett's The Maltese Falcon. Hammett's dialogue is so good that it made it into the movie almost straight from the page:
When a man's partner is killed he's supposed to do something about it. It doesn't make any difference what you thought of him. He was your partner and you're supposed to do something about it. Then it happens we were in the detective business. Well, when one of your organization gets killed it's bad business to let the killer get away with it. It's bad all around-bad for that one organization, bad for every detective everywhere.
And here, of course, is Humphrey Bogart, in the film that introduced so many of us to Hammett: