Second, the wonderful thing about NaNo is that it is not a publisher or an agent enforcing a deadline that will cost you money or possibly your whole book deal if you miss it. NaNo, though giving you some structure, is also beautifully flexible. You CAN make it to 50,000 words for NaNo. Start during November and end in January if you must, but you don't have to stop just because November 30th has arrived. Keep writing until that 50,000 words that you're calling so elusive is under your belt no matter what the calendar says. Believe me, you'll feel much better saying I didn't make 50,000 words UNTIL January 1st rather than just saying that you didn't make 50,000 words this year.
Third, if you've truly decided that 50,000 words is out of your reach, don't leave your goal for NaNo open-ended, a practice which is sure to lead to much fewer words than you are capable of putting out. Make a different goal for yourself and tell others about it to hold yourself accountable. Say instead, I've made a personal NaNo goal of reaching 30,000 words or of writing 3-4 short stories or something similar. That way you'll have an actual goal that your shooting towards and aren't just talking about a goal that you've decided that you're not going to reach.
We still have 9 days NaNoers. Go make words happen!