The novel clearly presents Ahab as a man who is tortured by his obsession and who does everything in his power to force his men to follow him to their destruction as they chase the white whale over the seas to their ultimate doom. In many ways, the novel is a testament to the danger of obsession and in particular a belief in fate that causes people to act in a way that endangers the lives of others. Note what Ahab says about his obsession in Chapter 37:
Come, Ahab’s compliments to ye; come and see if ye can swerve me. Swerve me? ye cannot swerve me, else ye swerve yourselves! man has ye there. Swerve me? The path to my fixed purpose is laid with iron rails, whereon my soul is grooved to run. Over unsounded gorges, through the rifled hearts of mountains, under torrents’ beds, unerringly I rush! Naught’s an obstacle, naught’s an angle to the iron way!
Ahab talks about fate by refering to his "fixed purpose," which he compares to a path fixed with "iron rails," arguing that this is the path on which his "soul is grooved to run." Ahab argues that his path, his pursuit of the white whale, simply must happen because that is what he is fated to do. He cannot see himself doing anything else and is completely unable to question fate and its control over his life. One of the themes of the novel is the extent to which fate is something that doesn't actually control lives, and men are presented as being able to shape their own destiny. This means that Ahab is using the argument of fate to cruelly manipulate his men, making them believe that their fate is welded to his own, and that any other action is impossible. Ahab's obsession is therefore presented as an example of individual needs and desires that are only achieved at the expense of his crew's life, which is shown to be wrong: he is only able to pursue those individual desires by manipulating and lying to his crew, and this ends in not only his death, but in the death of others. Such pursuit is never correct, the novel suggests.