The key to NaNoWriMo is the word count. Meeting the goal of 50,000 words. The best way to get there is to not edit, to not fix spellings or grammar, but to just keep the words coming.
There is another good reason not to edit. It is a distraction.
I can’t tell you how many times I’ve had the wavy red line under a word and I’ve paused to fix it – after all, it’s just a right click and select the right word – and lost my train of thought. It can happen that fast.
The mistakes will still be there when you come back to edit. Just keep writing. The world will not come to an end because you mizpelled a word or messed up a tense. Keep going. You’re almost done. Stay on pace, stay on track, you can do it.
Note: According to Chris Baty, founder of NaNoWriMo and author of many books including No Plot? No Problem! Revised and Expanded Edition: A Low-stress, High-velocity Guide to Writing a Novel in 30 Days, a good proportion of NaNoWriMo participants use procrastination to stall until the last four to six days of the month, then throw themselves into a frenzy to complete the 50K word count competition on overdrive. Even if you have been slacking, it is possible to write more than 10K words a day, if you stop editing and get out of your own way.