So I was watching the Robin Williams interview on the front page of Reddit earlier when I realized that what he does when he improvises is a pretty good analogy for writing, and for pushing yourself to write in particular.
What he's doing is rummaging in his stream-of-thought and just flinging handfuls of everything he digs up, hand over hand, without fear and without hesitation. If you'll watch, you'll see that not all of it makes sense. Not all of it is funny (though it is one of Robin's talents that he knows what's funny, so his flow is funnier than most). Some of it's even cringey--check out that pidgin English. There are a few duds that tumble out with the good jokes. But by and large, most of them are comedy gold, partially because of his off-kilter delivery. And, you know, comedy's going to offend somebody, especially a stand-up act. The best usually do.
When he improvs, he gets into the Groove, the Flow, and the jokes come out of him like a firehose. Wit is nothing more than being the fastest at making mental connections, and he's tapping a deeper level of fact-connections because he doesn't allow his output to be ruled by his inhibitions, his fears, or self-censoring. He's mainlining it straight from the source, no filter, no brakes. Imagine a switchboard operator, plugging and unplugging, plugging and unplugging. Robin is an octopus with a telephone wire in every tentacle.
But you see, the disadvantage he has against you is that you can do the same thing he does, but when you do it, you're typing it out, and when you're done, you can whittle it down to something a bit more coherent. And that's the secret--you've got to be fearless like Robin and just pour your brains out all over the page and get it out, get the words out of you and fix them later. All you cats in /r/Writing asking "how do I get motivation?" and "I'm afraid to write" and "What if nobody likes it?" and "how do I start?" and "what do I do now?": you've got to not be afraid of your brain, just cut the end open and squeeze it out. That's what some of the writers in here are getting at when they say "just start writing". Put your butt in the chair, your fingers on the keyboard, and take the training wheels off.
Well, that's as close as I can explain.
"Not really an explanation, but more of a...bizarre exploration."