It isn't difficult to find evidence of writers bemoaning harsh reviews, arguing over the validity of reviews, or blogging about what motivates them to write. The links I've posted in the previous sentence represent just one example of what is easy to find on the internet.
Why are these things so easy to find? Because we, as writers, really want to write. We love to write. But we doubt ourselves. The little devil of doubt sits on our shoulder whispering, But you have to clean up the living room. Your favorite TV show is on. You can write later. And it often works because we are afraid to fail. Afraid to write and not finish, afraid to write and be told it's not good, even though we know that we must write in order to finish and we must write in order to become better writers.
Harsh reviews of our work only magnify our fears. Yes, we can tell ourselves that everyone, even the best writers get bad reviews. And that is true. Yes, we can remind ourselves of all of the people who have been touched by our work and enjoyed it. But these reminders don't stop the little devil from using bad reviews as another whisper of doubt.
I recently read a quote by John Updike that encompasses these fears, but also gives a motivational answer to them:
"When I write, I aim in my mind not toward New York but a vague spot a little east of Kansas. I think of the books on library shelves, without their jackets, years old, and a countryish teen-aged boy finding them, and having them speak to him. The reviews, the stacks in Brentano's are juist hurdles to get over, to place the books on that shelf."
Find your motivational focus, one that can shut up even that little devil.
And feel free to motivate others by posting your motivation below.