This is a quote from the book "The Virtue Of Selfishness" by Ayn Rand
...ighest moral purpose.
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In psychological terms, the issue of man’s survival does not confront his consciousness as an issue of “life or death,” but as an issue of “happiness
or suffering.” Happiness is the successful state of life, suffering is the warning signal of failure, of death. Just as the pleasure-pain mechanism of man’s body is an automatic indicator of
his body’s welfare or injury, a barometer of its basic alternative, life or death — so the emotional mechanism of man’s consciousness is geared to perform the same function, as a baromete...