This is a quote from the book "The ​Virtue Of Selfishness" by Ayn Rand
... as the emotional fuel of man’s existence.

Just as the pleasure-pain mechanism of man’s body works as a barometer of health or injury, so the pleasure-pain mechanism of his con
sciousness works on the same principle, acting as a barometer of what is for him or against him, what is beneficial to his life or inimical. But man is a being of volitional consciousness, he ha s no innate ideas, no automatic or infallible knowledge of what his survival depends on. He must choose the values that are to guide his actions and set his goals. His emotional mechanism will w...
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