This is the one thing you absolutely cannot write 50000 words in thirty days without having. You will want to quit, many times. You may even find, if you do this often enough, that there are “discouragement milestones” that pop up regularly. For me, I’ve found that I usually want to quit about halfway through the available time window (two weeks in if I’m working all month, 1.5 weeks in if I’m trying to do it in three weeks), and around the 20000 and 40000 word milestones.
I can’t tell you how to muddle through to the end when you reach those discouragement milestones, partly because I don’t always muddle through. Outside of NaNoWriMo, the 40000 word milestone has defeated me three out of five times: I have tried to write a novel five times outside of NaNoWriMo, and three of those attempts are rough drafts 42000-45000 words long, that tell a more or less complete story.
You need to find a reason to keep putting down one word after another, a reason that matters to you. It might be your love for your characters or your setting or your message. It might be to prove to your friends that yes, really, you are a writer.
It might be sheer annoyance at the idea of failing. When I was younger, I played the Elder Scrolls computer games a lot, especially Daggerfall and Morrowind, and to a lesser extent Oblivion. Whenever they would crash to desktop, I would get so mad that I would relaunch the game immediately, from my last save point, which was usually pretty recent. (Compulsive saving/backup of any computer project on hand was the only major life lesson I learned from the Elder Scrolls franchise.)
I have had at least one NaNoWriMo where that “I won’t let myself be beaten by this” feeling was the main thing keeping me going in between the 40000 and 50000 milestones. The result was not my best work. But it taught me a lot about the kinds of things I enjoy writing and the kinds of things I don’t. And because I finished it, I knew I could finish it, and didn’t have to wonder about it afterwards.
It’s okay to quit NaNoWriMo. There’s not going to be any major consequences, unless your English teacher was requiring you to complete the challenge as a homework assignment, or you were trying to use the challenge to motivate yourself to deliver a book under contract. But you will probably wonder afterwards: “Could I have done it, if I had kept going?” or “What would that novel have been like if I had finished it?”
And about that kind of thing, you’re usually better off knowing for sure, than wondering. Good luck!