Evolution

If you chose at the last to fulfill the Youthful Naturalists' Destiny - whether he fully accepts it, or manages to subvert it - the Boatman recognizes the favour you have done him in securing his eventual freedom, and regrets that he must now inflict pain to you beyond the remit of his Duty. If, however, you chose to reject the Youthful Naturalists' Destiny, the Boatman recognizes that you have prevented - or at least, delayed - his heart's desire of freedom from his Duty, and sees here an opportunity to express his displeasure.