I believe actions speak significantly louder than words.
All the time I see people saying "I'm incredible", "I'm smart", "I'm good at X", but then have absolutely nothing to show for it. People will always blame something else for their failures, like "My friend did X", or "My teacher was a jerk" or "The economy is really bad".
Yes, they're all valid problems, but for people who have succeeded and have done something that you weren't able to do, they had the same problems and the same trials. If you have nothing to show for X, then you're not good at X, plain and simple. If you're "smart" but have bad grades, or haven't done any cool projects, or haven't achieved anything great, then you're not smart. If you're "Creative' but haven't written anything or published any music, or art, or stories, then you're not good at creative subjects. You're not good at anything until you actually have something to show for it.