I would think it's about being part of the mythology of the world and being a part OF the world, participating in it and caring for it.
then again, it could be about the piano. Maybe she is practicing for the concert next week and doesn't want to fuck that up?
Maybe she was just contemplating her role in life, I see her as a deep thinker like that, and the epiphany just hit her while going to get coffee that she is an artist part of the world and needs to not fuck it up (for the fans, for herself). It could mean a great many things I'm sure, but whatever it is I'm sure it's something more deep and not on the surface.