A man cannot be too careful in the choice of his enemies.
We can learn even from our enemies.
Use your enemy's hand to catch a snake.
Treat your friend as if he might become an enemy.
It is hard to fight an enemy who has outposts in your head.
Friends may come and go, but enemies accumulate.
An enemy is a person whose story we have not heard.
If you want to make enemies, try to change something.