"Everyone can do more than he thinks he can."
What you do with your life depends almost entirely on your self-concept. No matter how unreal the premise on which your self-concept is based, it makes real things happen to you. You may say, "I can do this" and "I can't do that," simply because of remarks that others have made about you. The chances are that you underestimate your own abilities.
Self-concepts might be compared to the houses built by the three little pigs. If a man builds up an image of himself that has no basis in reality, he's building his mental house of straw. A daydream about yourself that you don't follow up to make it come true can be blown down as easily as the house of straw.
Like the second little pig, you can build your mental house out of sticks, and it can also be blown down. If you build your self-concept on casual remarks made by others, you're building it out of sticks.
If you build your mental house out of bricks, who can knock it down? The wolves can come and howl at your door, but they will never knock down one single brick. Those bricks that build your self-concept can be academic or psychological tests showing exactly what you can do, personal experiences, or the encouragement of a loved one. If you have had personal experience in succeeding at something, no matter how small or big, you can build the house of your self-esteem on what you have done in the past. No matter how many failures you have had, somewhere in the midst of them was something you did well, which others praised.
Build your life on what you have already done successfully.