Writing is a solitary pursuit. There's something of the loneliness of the long distance runner in it. It often feels like an extreme sport. Hour after hour after hour of solitude. Time passing quickly if the work is going well, crawling if it's not.
Of course we all need criticism to guide us, and a healthy creative process has to include a time to solicit, consider and absorb criticism. However, there is real value in banishing criticism -- including self-criticism -- as you establish your creative process.