The confused interpreter
One of the great questions that kept philosophers occupied was, "what is the truth?" Can we ever know what the world really is? Whatever we see around us, it will always pass through the box that is our head, that is our heart (hormones, that is). Even our eyes, can we trust they are projecting the world as it really is? (Here's a little story for you: A man who sees everything narrower draws a tree. Then a person with healthy eyesight looks at the drawing and sees a perfectly normal tree. But this doesn't change the fact that the guy who made the drawing saw the tree differently than the other guy.)
Many people had theories about this, some said we could comprehend the truth, some said we couldn't, some said who cares, do we have an option anyway? The only theory I can link to its owner now (because it was my favourite - the middle ground) is Kant's. He said all the information goes through the processor that is our brain. Whatever limited information we actually get, our brain divides into little pieces, puts them together with what it already knew, rationalizes them, blows them out of proportion (with the help of hormones!) and in the end you get something that is new, different from what the world told you in the first place. The rays are refracted until they point in a completely new direction. And the most important information, the one that is most dear to you, the one that has the greatest consequences, is the one that gets distorted the most.
For example your perception of yourself. At any point in time, I perceive myself as someone stronger, weaker, smarter, stupider, prettier and uglier than I really am. The catch is that how you are determines how you see yourself and how you see yourself determines how you are. It is as if you put a broken mirror across an intact one, standing in between, trying to see yourself among infinite slanted versions of the truth.
Then all those misunderstandings that make the romantic comedies and soap operas all so grueling. The viewer knows the truth, she watches what both sides are going through, and she watches them interpret the limited information falsely, she watches the truth being distorted and hastily countered with the wrong reaction - how difficult is that? I know you know the feeling. You want to somehow go into the screen and poke the character and tell them what it really is. He loves you, stupid, don't go running off now! You'll ruin everything. He will not be able to stand you, he will give it up just because you thought he would.
Hence the self-fulfilling prophecy. Hence the power of positive thinking. The secret. It actually has nothing mystical to it, it all makes sense. You are pessimistic, you interpret the information wrong, you see yourself weak and stupid, you think the others see you weak and stupid, you distrust them, you distrust yourself, you don't apply to your dream job, you don't pursue your dream boy, you leave them before they leave you, and then you end up losing the boy, losing the job, only because you thought you would. You leave yourself, as Alanis Morissette says, you don't stand behind yourself anymore. Now I figured it all out without even having read the secret ;)