We know from experience that friendship—true friendship—isn't for everyone: some people are jerks. Aristotle understood this, too. In order to be a good friend, he says, we have to possess the "characteristic" or virtue for it.
We have to be lovable, which means that we have to have something admirable about us, something that other people can love. And what's more, we have to be more interested in loving than being loved. Selfishness isn't going to cut it in Aristotle's Nicomachean Ethics.
Aristotle details three types of friendships—of usefulness, of pleasure, and complete friendship. Of these three, only complete friendship is the real thing. In it, each person sees himself reflected in the other. Justice exists perfectly between them. The friends love each other for what they are, not for any external goods they can give.
It's a rare thing, since most people can't meet these criteria…but we have to try for it since the pleasure of a good friendship is absolutely necessary for ultimate human happiness.
Questions About Friendship
What are the types of friendship outlined by Aristotle?
Can corrupt people be/have friends?
Why is it important for friends to love themselves first?
What's the correlation between the level of justice in a regime to the types of friendships that can flourish in them?
Chew on This
Complete friendship is rare because it is really impossible to achieve, according to Aristotelian standards.
Friendship is the basis for all relationships in Aristotle's concept of society.