I may have failed to reach 50K words, but there are still reasons to consider this a success!
Today is the last day of my seventh NaNoWriMo. I started participating in this challenge back in 2006, and I've done it every year since, though I've failed to reach 50K words more often than not. Although I'd won last year, and again in August when I participated in the summer session ("Camp" NaNoWriMo), this November I failed to reach my 50K word goal.
However, I don't consider this NaNoWriMo to be a failure.