Another line with a complex and foreshadowing double meaning. "In the end," Nostromo's undoing is indeed because of darkness: Viola shoots him because it is literally too dark to identify him. But I also see a symbolic meaning here, regarding darkness as isolating subjectivity. Nostromo's successful career has been based on the dream-ideal of reputation: how he is seen subjectively by others. The darkness was indeed his "protection." But when he steals the silver, he uses his reputation as a disguise; the same subjective dream-ideal becomes a cloak for the "undoing" of his integrity.