What greatness? This is clearly Conrad speaking rather than the sailor. He has already avowed that he has no interest in crime as such, so he cannot be speaking of any mastery in theiving. The oblique insistence on "greatness" here is of a piece with the novel's many references to "the magnificent Capataz de Cargadores." What makes Nostromo magnificent and the sailor great in Conrad's eyes is, I believe, their ability to, at the right moment, take a single sideways step completely out of their appointed and sustaining social role, committing themselves to the solitude of a grandiose dream.