I can't be the only writer on the board who struggles with this, so open thread for coping/affirmation mechanisms ahoy!
I'm fortunate in that I have a very engaged and vocal readership, but I've noticed that if one person shreds my writing in a "I hate everything about it, trash it all and start over" kind of way, I tend to take that to heart really seriously and forget the twenty other people who said they loved it. I suspect this is a human bias condition where I'm remembering criticism and forgetting praise (or rationalizing it as people being nice, polite, etc.).
So. What are your mechanisms for continuing to write in the face of bad reviews, lackluster sales, angry beta readers, and so forth? SHARE.