D.K.
You HAVE to keep reminding them that NO ONE is good at everything AND.....that no one is perfect. Remind them that MANY inventions, etc. are the result of mistakes. There is a book about them that you might want to get. Keep reminding that VERY few people get it right the first time. It takes practice and practice and practice....at just about EVERYTHING
When you make a mistake, acknowlege it in front of him, if the opportunity is there and appropriate. He'll realize that he can accept "less than perfect".