“beware of your most implacable enemy-yourself.”
“Beware when your enemy's too easily defeated.”
“Enemies of the Heir, beware! You'll be next, Mudbloods!”
“I am your dwarf.I am the enemy within.I am the boss of your dreams.See. Your hand shakes.It is not palsy or booze.It is your Doppelgangertrying to get out.Beware...Beware...”
“The greatest enemy is conquered only in death. Your greatest enemy is yourself.”
“Know the enemy and know yourself; in a hundred battles you will never be in peril. When you are ignorant of the enemy, but know yourself, your chances of winning or losing are equal. If ignorant both of your enemy and yourself, you are certain in every battle to be in peril.”