A Wizard of Earthsea
How we cite our quotes:
It was not his own life that he bargained for. One mastery, and only one, could he hold over the dragon. He set hope aside and did what he must do (5.85)
Perhaps inspired by Nemmerle – who carried out his duty even though it came with a price – Ged does something really heroic here: the dragon Yevaud has promised to help him with his personal problem (the shadow monster), but Ged has a particular duty to the people of Low Torning. Ged might have been a selfish kid (running off to play rather than, say, working with his dad), but he seems heroic and selfless now.
He went to the Sea-House of Serd, where travellers and merchants ate together of good fare provided by the township, and might sleep in the long raftered hall: such is the hospitality of the thriving islands of the Inmost Sea. (6.19)
We often think of duty in this book as things you must do that are related to your job – if you're the wizard of a village, then you're supposed to heal the village-people, etc. But here's an example of something that we might call a duty towards strangers and guests: the town feeds people who pass through because there's a general responsibility to be hospitable hosts. This contrasts pretty strongly with how Serret treats Ged when he's her guest at the Court of the Terrenon.
"Master, I go hunting." (7.118)
In this short sentence, Ged expresses two duties: 1) he has to stop the shadow from hurting more people, and the best way he can do that is to hunt the shadow; and 2) he has a duty to Ogion, his master, who's his real teacher and the one person who always gives him good advice.