"In any hour and issue of his life, man is free to think or to evade that effort. Thinking requires a state of full, focused awareness. The act of focusing one’s consciousness is volitional. Man can focus his mind to a full, active, purposefully directed awareness of reality — or he can unfocus it and let himself drift in a semiconscious daze, merely reacting to any chance stimulus of the immediate moment, at the mercy of his undirected sensory-perceptual mechanism and of any random, associational connections it might happen to make.

When man unfocuses his mind, he may be said to be conscious in a subhuman sense of the word, since he experiences sensations and perceptions. But in the sense of the word applicable to man — in the sense of a consciousness which is aware of reality and able to deal with it, a consciousness able to direct the actions and provide for the survival of a human being — an unfocused mind is not conscious.

Psychologically, the choice “to think or not” is the choice “to focus or not.” Existentially, the choice “to focus or not” is the choice “to be conscious or not.” Metaphysically, the choice “to be conscious or not” is the choice of life or death."

Ayn Rand, The Virtue of Selfishness, 20