What Adam Smith said is that individual actors profit by fulfilling their customers needs. Better profits are made by better fulfilling those needs, thus, as if there were an invisible hand, different actors cooperate or compete in ways which tend toward efficiency. Social order is a direct result of this market liberty to interact, because violence is extremely inefficient and wasteful of resources. While you're wasting your time on vendetta, your competition is undercutting your prices.

Note "tend" toward effiency. No market interaction is ever completely efficient, because by the time you've figured out how to fulfill someones wants, they've changed their minds. Basic human nature.