In the province of the mind, what one believes to be true either is true or it becomes true.
John Lilly
[See also what Paul Simon said on essentially the same topic.
There are lots of examples of this. It helps explain why there are so many religions that have incompatible "immutable truths". It helps explain advocates of socialism even after the deaths of tens of millions and the misery of 100's of millions by those attempting to build a "workers paradise". And in my favorite example it helps explain why Chicago politicians put up such an irrational defense in the McDonald v. Chicago case (via Dave Hardy)--Joe]