The popular American viewpoint is that one's possibilities are unlimited. Every child can grow up to be president, planning on becoming immensely famous and successful is a laudable goal, everyone is creative and talented, and we are all beautiful. In shows like American Idol, when the contestants lose, they are still told "Don't give up on your dream" by teary-eyed judges: they can still succeed at becoming world-famous singers, no matter what!
I don't believe this at all. In fact, I think it's really harmful.
The main criterion for becoming a wise and mature person is self knowledge (thus the inscription at the oracle of Delphi: KNOW THYSELF). This means a true knowledge of your strengths and weaknesses, and also an understanding of how these rank vis-a-vis other people. This sounds easy enough, but it's actually one of the most bitter realizations that comes with increased wisdom, because it means admitting that you are inadequate or incompetent. It also means accepting that many things are not possible (I will never sing like Adele).
Of course I don't always do a good job at this task, but I try my best. Sometimes this shocks people who have bought into the whole "You go, girl!" worldview. I remember telling someone that I wasn't creative, and they broke into horrified denials, as if I'd just said I was too ugly to live or something similar.
The truth is, I'm not very creative (especially artistically). I appreciate it in others, and think it's a immensely valuable quality, and that is exactly the reason I know I lack it. Naturally I would like to be immensely talented (like Beethoven or Caravaggio or Dostoevsky), or even someone who constantly comes up with new and provocative ways of seeing the world (like my husband). Living in denial of this fact isn't going to make me creative though; it will just prevent me from viewing myself honestly, and understanding the good qualities I do have.
Other things I'm not good at: physical activities (I am slow, clumsy, and it's very difficult for me to learn new physical skills: I didn't learn how to ride a bike until I was 20); being tactful, diplomatic, and socially smooth; being patient, especially when it comes to waiting for things; and being funny (which I think you can tell from the blog!). This doesn't mean I should just give up on doing these things (all of them are important!) but I am always going to be significantly worse at them than average, and making even a little progress is going to be harder for me than most people.
The flip side of this is recognizing your strengths. Sometimes this is hard because it means saying that you are better than other people, which sounds so conceited, even when (especially?) if it's true. (I wrote about this in terms of intelligence a while ago.) I understand why it's not a good idea to go around bragging about your beauty or social skills or whatever, but the problem can be that if you can't admit something in public, you can't admit it to yourself either. Beautiful people who think they're ugly (many very attractive teenaged girls for instance) are suffering from this problem. Lots of smart or talented people handicap themselves in various ways, and never reach their full potential partly for this very reason (I think this is called "hiding your light under a bushel").
Everyone would be better off if they were honest. The world would be better off too, because then we could all acknowledge that some people are smarter or stronger or better leaders or funnier than others, and then have the ones with the right skills pursue the proper tasks. Instead, everyone aims at a well-rounded mediocrity, and that's who succeeds (example: pretty much all politicians).