Start at 9:08
Steve Donoghue is a book nut who discusses books and writing on his YouTube channel, and in this video, he encourages writers to start their NaNoWriMo with something I found encouraging -- and I hope it'll encourage other writers whether they're doing NaNoWriMo or not.
"Get it done." Set a word goal and just get it done. If it's 2,000 words a day, then write 2,000 words. Don't fret over how good they are, or if the grammar is correct...or anything about it, really. Just get it done. That's the goal: get it done, not right.
Another encouraging quote I found that comes not from him, but from a long-dead Roman Emperor:
“Do what nature demands. Get a move on--if you have it in you--and don't worry whether anyone will give you credit for it. And don't go expecting Plato's Republic; be satisfied with even the smallest progress, and treat the outcome of it all as unimportant.” - Marcus Aurelius, Roman Emperor from 161-180 AD in his personal journals.
Just get it done, and don't expect yourself to be the next Plato. You don't have to be the next Plato.