My father used to say that if I told myself I was smart and liked homework, then my brain would respond accordingly. Apparently, recent research has shown that this might actually be true:

Researchers found that when older volunteers took a series of cognitive tests after being given hints that their age might affect the results, they did less well. The study, which appears in Experimental Aging Research, was led by Thomas M. Hess of North Carolina State University.

-NT Times, “Reminders of Age Undermine Memory”

When thoughts manifest into beliefs, beliefs intertwine with reality.