He's not even one of my favorite author's but he sure touched me with what he says.. So, I had to quote it here.
“Now, what I’m thinking of is, people always saying “Well, what do we
do about a sudden blockage in your writing? What if you have a blockage
and you don’t know what to do about it?” Well, it’s obvious you’re
doing the wrong thing, don’t you? In the middle of writing something you
go blank and your mind says: “No, that’s it.” Ok. You’re being warned,
aren’t you? Your subconscious is saying “I don’t like you anymore.
You’re writing about things I don’t give a damn for.” You’re being
political, or you’re being socially aware. You’re writing things that
will benefit the world. To hell with that! I don’t write things to
benefit the world. If it happens that they do, swell. I didn’t set out
to do that. I set out to have a hell of a lot of fun.
I’ve never worked a day in my life. I’ve never worked a day in my
life. The joy of writing has propelled me from day to day and year to
year. I want you to envy me, my joy. Get out of here tonight and say:
‘Am I being joyful?’ And if you’ve got a writer’s block, you can cure it
this evening by stopping whatever you’re writing and doing something
else. You picked the wrong subject.” — Ray Bradbury at The Sixth Annual
Writer’s Symposium by the Sea, 2001
From: 13 Famous Writers on Overcoming Writer's Block
The whole article is good. Every writer on the list has something helpful, motivational or just plain "kick you in the butt" to say.