Does it ever matter why a friend isn't a good friend or does it only matter that they aren't/ weren't?

Friendship of any kind is to be valued and enjoyed and not judged.  I read often on this site how people feel they are owed something by others but I can only see such feelings as their self-interest talking and getting the upper hand.  We find each other and we enjoy each other's company and that should be enough.  We all have our own lives to live.