Because some people really do get very depressed on the way they look. Others blow it off because they know that they're gorgeous, but others live there life wishing they were the opposite sex. It's normal for plenty of guys/girls to go through this. Some guys, have the mind of a girl, and some girls have the mind of a boy, which changes them to get a sex change. It's not stress that causes it, it's themselves. They choose to do it. There is nothing wrong with it, yeah granted they should stay the way they were born but if they think they were born to be the opposite, let them be.