Two things I have learned about writing over the past 10 years:
1) The Muse exists to make you feel good; nothing more. Sometimes the prose bursts fully-formed from your fingertips. Sometimes you must laboriously yank every word kicking and screaming from the bottom of your brain. And in most cases, when you re-read the manuscript a week later, it's impossible to tell which prose is which.
2) The primary challenge in writing fiction lies, not in generating new ideas, but in knowing which ones to throw out. Every writer I know has a desk drawer overflowing with notes, outlines, and half-formed story ideas. Inspiration is not difficult to come by. But learning to recognize the one idea out of the thousand that has stuff of great fiction buried inside it; learning to reject the mediocre ideas and concentrate only on the ones that speak to your soul -- that's hard.