I've been reading Keith Johnstone's brilliant little book, Impro: Improvisation and the Theater, which as you can probably guess is about acting. But it's about much more: it's about creativity, and teaching, and anthropology, and psychoanalysis, and writing dialogue, all in about 150 pages.
Somewhere in the middle of the book he drops this gem:
Writer's block is never because you cannot come up with an idea. Writer's block is when the story that wants to come out is blocked by the part of you anxious that it will be too personal and will reveal the truth: that you, like everyone else, are not quite so sane and secure as you pretend.
Put that on a post-it note and keep it next to your writing desk. The next time you have writer's block, feel a little shame that you're not quite courageous enough to tell the truth.