Say what you will, the concept is not Biblical in origin, save for a few cherry picked verses here and there.
People want to believe they can cause change through their thoughts. That's the basis of "the law of believing". If it were true, the world would be in a constant state of chaos, with conflicting thoughts cancelling each other out and confounding reality. (eg: I want it to rain, you don't. Who wins?) .....ad infinitum.