You probably know them; they live between us, hiding in their closets only to come out of the shadows when it's too late to stop them. Yeah, I'm talking about the lone wolves.
Maybe you call them in other names, maybe you don't call them at all, but they are always there: those characters that just don't get along with their groups, those characters who think only about themselves, that feel alien to the group.
Those characters, whose players defend them with saying: "That's what my character will do", and you don't have anything to say to them, against it, just because you know it is true, because you know you made a mistake.
And that's one of the purposes of the background: to identify these things and to stop it before it can happen, to cure the disease before it rages on. Because no wolf survives alone, for that they are in group, to survive and to prosper before they'll all die, because "together we stand- divided we fall".
There is no real tip in here, just 2 things to consider: The first is to look for these things in the background. Characters that have nothing in the world, or characters who have problems connecting with people should be left out already in this stage.
The second is to remind those players that it is a social activity, to remind them that they're not alone in the world, and to remind them that no wolf survives alone, that living without anyone in exile is a more moral way to sentence someone to death.