Every time I think about writing a book, I question whether I could write anything that I didn't learn from better books already. Looks unlikely.

I don't know you, but the same is true for nearly anything you could create. Software included. The difference is, you go out of the way to fill whatever gap is unfilled. Maybe you'll never be able to write a better Young Girl Becomes Werewolf As Metaphor For Growing Up YA Novel, but perhaps your happens to have a main character that not only is Young Girl Becomes Werewolf, but Young Girl With Problem Burping That Becomes Werewolf, and that connects just right to a certain group of people that never knew they needed this particular book.

Same for weird little dumb tools/libraries you could publish on github, songs you could write, etc.