An enemy is an enemy of himself, even if he appears to attack others as well. You will most often find self-destructive tendencies, illnesses and physical problems on people that are stuck on being an enemy. In agreeing with an enemy of oneself another can be given a wonderful opportunity to become the same for himself.
An enemy is not pleased at his well-being and he is not pleased at the well-being of others, either. Both conditions can be hidden.
A kind person who wants to be good to others can fall into the trap of trying to make enemies happy. One cannot make an enemy happy without becoming an enemy of himself too. An enemy will not like another’s well-being and he will try to make that another get worse. That doesn’t have to be done through directing fighting, but when another is or does something good, he will be shown disapproval, intimidation or even disgust so as to think he is not or he doesn’t do anything good. What he is and what he does will get twisted to mean something worse than what he is and does. If one is beautiful she can be called a slut, if one is proud he can be called arrogant, if one is clever and can be called a nerd, if one chooses carefully who he talks to he can be called snobby, and so on…
It is necessary for one to not need good feedback whether he is good or not, whether he does good or not, otherwise he is liable to fall into endlessly doubting (at first) himself, or even harming himself in the end, and thus becoming an enemy too.