The chain is only as strong as its weakest link, for if that fails the chain fails and the object that it has been holding up falls to the ground.
Well, the first rule is that you can’t really know anything if you just remember isolated facts and try to bang ‘em back. If the facts don’t hang together on a latticework of theory, you don’t have them in a usable form. You’ve got to have mental models in your head. And you’ve got to array your experience, both vicarious and direct, on this latticework of models.