Willpower

The latter was the eternal, living principle or soul in him; and in sleep, being for the time dissociated from the characterizing mind, which at other times employed it for its outer vehicle or agent, it spontaneously sought escape from the scorching contiguity of the frantic thing, of which, for the time, it was no longer an integral. But as the mind does not exist unless leagued with the soul, therefore it must have been that, in Ahab’s case, yielding up all his thoughts and fancies to his one supreme purpose; that purpose, by its own sheer inveteracy of will, forced itself against gods and devils into a kind of self-assumed, independent being of its own. Nay, could grimly live and burn, while the common vitality to which it was conjoined, fled horror-stricken from the unbidden and unfathered birth.