“Hold thought steadfastly to the enduring, the good, and the true, and you will bring these into your experience proportionately to their occupancy of your thoughts.”

Disputed

1840s, Essays: First Series (1841), Self-Reliance
Context: I read the other day some verses written by an eminent painter which were original and not conventional. The soul always hears an admonition in such lines, let the subject be what it may. The sentiment they instil is of more value than any thought they may contain. To believe your own thought, to believe that what is true for you in your private heart is true for all men, — that is genius. Speak your latent conviction, and it shall be the universal sense; for the inmost in due time becomes the outmost, — and our first thought is rendered back to us by the trumpets of the Last Judgment.

Source: The Secret

§ IV
1910s, At the Feet of the Master (1911)
Context: See what gossip does. It begins with evil thought, and that in itself is a crime. For in everyone and in everything there is good; in everyone and in everything there is evil. Either of these we can strengthen by thinking of it, and in this way we can help or hinder evolution; we can do the will of the Logos or we can resist Him. If you think of the evil in another, you are doing at the same time three wicked things:
(1) You are filling your neighbourhood with evil thought instead of with good thought, and so you are adding to the sorrow of the world.
(2) If there is in that man the evil which you think, you are strengthening it and feeding it; and so you are making your brother worse instead of better. But generally the evil is not there, and you have only fancied it; and then your wicked thought tempts your brother to do wrong, for if he is not yet perfect you may make him that which you have thought him.
(3) You fill your own mind with evil thoughts instead of good; and so you hinder your own growth, and make yourself, for those who can see, an ugly and painful object instead of a beautiful and lovable one.
Not content with having done all this harm to himself and to his victim, the gossip tries with all his might to make other men partners in his crime. Eagerly he tells his wicked tale to them, hoping that they will believe it; and then they join with him in pouring evil thought upon the poor sufferer. And this goes on day after day, and is done not by one man but by thousands. Do you begin to see how base, how terrible a sin this is? You must avoid it altogether.

Source: Hardboiled Wonderland and the End of the World (1985), Chapter 24: Shadow Grounds

Source: The Kings of Clonmel

Twelve Virtues Of Rationality http://yudkowsky.net/rational/virtues
Context: Do not flinch from experiences that might destroy your beliefs. The thought you cannot think controls you more than thoughts you speak aloud. Submit yourself to ordeals and test yourself in fire. Relinquish the emotion which rests upon a mistaken belief, and seek to feel fully that emotion which fits the facts. If the iron approaches your face, and you believe it is hot, and it is cool, the Way opposes your fear. If the iron approaches your face, and you believe it is cool, and it is hot, the Way opposes your calm. Evaluate your beliefs first and then arrive at your emotions. Let yourself say: “If the iron is hot, I desire to believe it is hot, and if it is cool, I desire to believe it is cool.”

Source: Promulgation of World Peace, p. 453
Context: Act in such a way that your heart may be free from hatred. Let not your heart be offended with anyone. If someone commits an error and wrong toward you, you must instantly forgive him. Do not complain of others. Refrain from reprimanding them, and if you wish to give admonition or advice, let it be offered in such a way that it will not burden the bearer. Turn all your thoughts toward bringing joy to hearts. Beware! Beware! Lest ye offend any heart.

depends on the situation
The Great Master of Thought (Amen- Vol.3), Observing management