This is a quote from the book "The Virtue Of Selfishness" by Ayn Rand
...lest form? By means of the physical sensations of pleasure or pain. Just as sensations are the first step of the development of a human consciousness in the realm of cognition , so they are its
first step in the realm of evaluation.
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The capacity to experience pleasure or pain is innate in a man’s body; it is part of his nature, part of the kind of entity he is. He has n
o choice about it, and he has no choice about the standard that determines what will make him experience the physical sensation of pleasure or of pain. What is that standard? His life.