Love. Fall in love and stay in love. Write only what you love, and love what you write. The key word is love. You have to get up in the morning and write something you love, something to live for. ↗
It is hard to rationalise or explain why you love what you love. But I have always been interested in science and maths, and in high school I was struck that you could use maths to understand nature and science. ↗
I have friends who wear Star Wars costumes and act like the characters all day. I may not be that deep into it, but there's something great about loving what you love and not caring if it's unpopular. ↗