A paranoid, every-man-for-himself sort of world can cause you problems here. If no one has any reason to trust or confide in other people, then non-player characters (NPCs) aren't going to want to trust or confide in the PCs. The PCs aren't going to be as likely to poke their noses into other people's business. This cuts off a very valuable avenue of motivation for the GM! If you have such a world, carefully balance this with plenty of other ways for the PCs to get involved in things.