Steven Pressfield, from War of Art.
I’m gonna stop quoting it on here (for now) as I I highly suggest you pick it up and give it a read yourself, Reading Rainbow-style. That said, big thanks to kellysue for suggesting it on her earlier Tumblr post I added a few reading suggestions to. It’s already been a hugely productive, inspiring read.
Amazing book! Just sit down or get out there and do what it is you love. What you feel compelled to do. Just do it.