“If you are your own worst enemy, don't do yourself any favors.”

Source: Love in the Afternoon

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

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

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!

Promoting "Crocker's Rules" at SL4 (c. 2000) http://www.sl4.org/crocker.html
Context: Declaring yourself to be operating by "Crocker's Rules" means that other people are allowed to optimize their messages for information, not for being nice to you. Crocker's Rules means that you have accepted full responsibility for the operation of your own mind — if you're offended, it's your fault. Anyone is allowed to call you a moron and claim to be doing you a favor. (Which, in point of fact, they would be. One of the big problems with this culture is that everyone's afraid to tell you you're wrong, or they think they have to dance around it.) Two people using Crocker's Rules should be able to communicate all relevant information in the minimum amount of time, without paraphrasing or social formatting. Obviously, don't declare yourself to be operating by Crocker's Rules unless you have that kind of mental discipline.
Note that Crocker's Rules does not mean you can insult people; it means that other people don't have to worry about whether they are insulting you. Crocker's Rules are a discipline, not a privilege. Furthermore, taking advantage of Crocker's Rules does not imply reciprocity. How could it? Crocker's Rules are something you do for yourself, to maximize information received — not something you grit your teeth over and do as a favor.

§ 132
Major attributed works, Ratnāvalī (Precious Garland)

Source: 1984