Many believe that after they've made a self-portrait, that they are somehow 'done' with self-portraits. The ole "been-there-done-that" mindset (which drives me crazy!) I explain that Frida Kahlo and Vincent Van Gogh didn't just make one self-portrait; between the two, they've probably made hundreds! They don't all work-some were probably considered "failures" by the artists-but they were all worth doing. Because something could be learned by all of them.
This BBC Magazine article, How Creativity is Helped by Failure, is worth a read.