When my kids exhibit self-doubt I tell them that they are punching themselves in the nose. They all know this story I told them.
The story I tell starts once upon a time there was a princess (or prince) who woke up one day to find a small pimple on her nose. All through breakfast nobody said aything but it was all she could think of. She thought that everyone at the table could see her nose and was simply being polite. Immediately after breakfast, she ran to the bathroom to check her nose again. She decided to pick at the pimple and as she did it began to bleed - so that day she had to go to school with a bandage on her nose.
All that day she adjusted her hair so that it would take away attention from her nose, but her hair got in her eyes and she walked into a pole. Smack on the nose. Now her nose was in pain and started to swell. That evening at home she looked even worse. She took off the bandage and the pimple was mostly gone but now her nose was very sore and a little bit red. The following morning her nose was pretty much back to normal but it felt horrible. She put extra makeup on it, just to make sure and she wore some very loud colors to distract from her face.
All this time, people noticed she was acting strange but not about her nose. Only she knew that her nose was making her behave this way - and yet she never told a soul because by now her story was just too embarrassing. Sure enough some kids laughed at her clothes and pointed their fingers at her. She went into the bathroom and cried. She was so mad at herself that she began to punch herself in the nose. She ran home and checked again in the mirror. She had given herself a bloody nose. The more she tried to fix her nose, the more things went wrong, the more she punished herself, the more embarrassed she became. It went on for a week until she finally broke her own nose. Now it became obvious to everyone that her nose was indeed ugly, swollen and slightly crooked.
There are several lessons to be learned from this story. The first is that perfect is the enemy of good. The second is that vanity is self-destructive. The third is not to second-guess what people think about you. The most important is that you can be your own worst enemy because only you know exactly what torments you most.
The story can obviously be changed around or extended to more tragic lengths, but I always like the punch in the nose idea because as a kid I had a lot of fights. I would come home after crying with my face in pain, and unless I had a black eye or my nose was still bleeding, I could feel the pain but nothing would show. The same thing was true after a really good game of football. And so it always fascinated me that people could feel pain and not convey it - that nobody really knows what's going on with you unless you tell, that overcoming the fear of telling releases you from the pain of your insecurity.
Of course you can become a pain in the ass, but that's another story.