There's the idea of the Dark Forest, that alien civilisations, when confronted with other intelligent life, have to make the assumption that those others can't be trusted not to become a threat, so that the only sensible thing to do is a pre-emptive strike. This would lead to the only surviving civilisations being the ones who keep their heads down and make sure they don't get noticed.

To be honest, I think that's a bunch of crap, and one of the reasons why I didn't really enjoy the Three Body books as much. The other one being the automatic assumption that there'd be a substantial amount of doomers who would collaborate with aliens to help them invade the earth and decimate mankind. Yeah there are wreckers around, but the motivation of these wallbreakers and Trisolarian sympathisers just seemed too damn artificial.