I had the interesting experience of cleaning out my daughter's room a few weeks ago (which is always interesting because I'm not a good housekeeper. I never know what I'll find.) But one of the things I discovered was her daily journal from her 1st grade class last year.
The idea being that each student was required to write *something* every day. No specific topics - as long as they wrote an entry, they were all set. Lucy's topics went from werewolves to ninjas and everything in between. (Usually with interestingly detailed illustrations.)
Until I got to the page with this illustration. The caption, which is cut off here, reads:
"I don't want to write today because I have nothing good to write about. I just can't think about something good to write."
Out of the mouths of babes, indeed.
My opinion here is that if a child who is pretty much unlimited in her imagination and unfettered in her writing has a bad day where she can't think of anything, it only makes sense that those of us who do it for a living are going to run into that exact same wall, so you shouldn't beat yourself up too hard over it. (And for the record, the next day her journal was all about tigers and wanting to be one, so...there we go.)
That being said, deadlines are tricky things, so letting a bump in inspiration become an actual block can become ugly.
Sometimes it's about figuring out what's causing the block - is it a scene or a character that isn't working? A chapter? Like KAK mentioned the other day - blocks can often come when you're trying to force a story in a direction it doesn't want to go. Sometimes it's good to just sit and "listen" to what it's telling you. (Which for me, usually involves a lot of hot showers. I think/brainstorm my best there. Not sure why - maybe because it's comfortable and low pressure and I'm not motivated to do anything but take care of myself. Between the mom thing and the job thing, sometimes those precious few minutes are all I get - so I take full advantage of them.)
I'm not the only one who does the shower/bath as inspiration thing either - I know several writers who keep bath crayons nearby to write down ideas on the tiles if they think of any, so there you go.
If a shower doesn't shake anything loose, I usually end up going to plain old pen and paper and sketching out ideas that way. Doodles, maps, ideas. Sometimes the physical act of sketching out thoughts is enough to do the job - and usually after a day or so, I'm good to go. (Or I move on to a different scene that I *do* know how to write.)
If things still aren't flowing, sometimes I find it's better to just remove myself from the project all together for a few days - maybe work on a different project, or take some time out to read or play a video game, though that has to be tempered, because it's realllllly easy to start tumbling down that "I can't write tonight I'm not insppppirrrred" hill. So usually I set a timer or give myself one evening to just fuck off with the assumption that I'll be back at it the next morning - sometimes the brain just needs a break.
Which brings me to a final point - sometimes the mind is willing, but the flesh is weak. If you find yourself nodding off or just too plain exhausted to write (and I'm talking eyes burning or passing out at the keyboard levels), maybe it's time to to physically get some rest - a day or two of catching up on sleep can be frustrating, but it's *way* better than working yourself into a lousy head cold over it.
Ounce of prevention and all that.
Or, you know. Write about being a ninja.