This answer recognizes that motivation comes from within a character.
Real life is like that too.
For example, let's say a friend of yours decides to visit the Big Island. If you happen to know that your friend has relatives in Hilo and wanted to visit them, then you understand your friend's motivation. Now think about your motivation. Maybe that you are curious about astronomy and want to learn something about it. Or perhaps you have only a little interest in astronomy, but need the credit because it enables you to go on and study another subject that really interests you.