Harry has a big destiny; that much is clear in Harry Potter and the Sorcerer's Stone. And going from being the kind of kid who gets stuffed into lockers to being the sole hope for the whole Wizarding World can instill a real sense of duty in you.
Harry suddenly has purpose, friends, and even some real live power—and he's super-grateful. So grateful, in fact, that he's willing to take on this huge task (which is going get a whole lot huger in subsequent movies) in order to protect these wonderful new things in his life.
Questions About Duty
What rules do Harry and his friends have to break in order to do their duty? What kinds of risks do they run by doing so?
What kinds of duties do the adults have in the film have? How well (or poorly) do they fulfill them?
What does Harry owe this magical world he's just discovered? What does this world owe him in return?
Does Voldemort express any kind of duty? What does this say about his nature?
Chew on This
Duty is what defines heroism in this world.
Duty can be both good and evil, depending upon who's showing it and what their ultimate intentions are.