I don't think I would ever have brought the thoughts about that useless shelf above our sink out of the bathroom if it wasn't for writing. It was just something that came to my mind every time I saw it and was already forgotten the time I stepped out from the bathroom.
But after writing daily for so many years one of the things I've learned is paying attention to such little things. There are always potential topics lurking around when you keep your eyes open. They might not be that interesting on themselves, but they might incite some more interesting thoughts.
Everything is worth writing. It's another matter if all that is worth reading. But the fact is: there is always something to write about. Having nothing to write about is a bad excuse for not writing. There are potential topics everywhere. Just have a look around you and pick one.