I consider myself to be a fairly simple person. If you are wondering whether I consider you to be a friend or an enemy just remember that I am trying to get a bunch of things done. That makes it all so much simpler.
If you are assisting me - in some way - to get my things done then you are a friend.
If you are holding me back from getting my things done, then you are an enemy.
Sure it does mean that people are friends and enemies in all sorts of rotations. But it really is as simple as that. And as complex.