“But the worst enemy you can meet will always be yourself; you ambush yourself in caverns and forests.”
Source: Thus Spoke Zarathustra. The Way of the Creator.
Context: But the worst enemy you can meet will always be yourself; you ambush yourself in caverns and forests. You solitary one, you go the way to yourself! And your way leads you past yourself and your seven devils! You will be a heretic to yourself, and a sorcerer and a soothsayer, and a fool, and a doubter, and a reprobate, and a villain. You must be ready to burn yourself in your own flame; how could you rise anew if you have not first become ashes!
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Friedrich Nietzsche 655
German philosopher, poet, composer, cultural critic, and cl… 1844–1900Related quotes
“If you are your own worst enemy, don't do yourself any favors.”
The Well-Spoken Thesaurus (2011)

““Be yourself” is about the worst advice you can give some people.”
Thomas L. Masson, The Book of Today, (1923), as cited in: Clifton Fadiman (1955) The American treasury, 1455-1955. p. 791.

Variant translations
If you know others and know yourself, you will not be imperiled in a hundred battles; if you do not know others but know yourself, you win one and lose one; if you do not know others and do not know yourself, you will be imperiled in every single battle.
Know your enemy and know yourself, find naught in fear for 100 battles. Know yourself but not your enemy, find level of loss and victory. Know not thy enemy nor yourself, wallow in defeat every time.
Literal translation: Know [the] other, know [the] self, hundred battles without danger; not knowing [the] other but know [the] self, one win one loss; not knowing [the] other, not knowing [the] self, every battle must [be] lost.
Source: The Art of War, Chapter III · Strategic Attack

“Always be yourself, unless you can be Batman, always be Batman.”

Question period following Lecture 11 of Leonard Peikoff's series "The Philosophy of Objectivism," 1976