While I'm sympathetic to the idea that "you are likely to begin believing things you say to yourself frequently, and furthermore you are likely to act in ways to make these beliefs come true," I'm not sure I'd use Scott Adams as the prototypical purveyor of this idea. He is known to have beliefs difficult to characterize as "rational," notably a belief in intelligent design creationism. The Wikipedia also cites him as being a hypnotist and a vegan; these are not inherently irrational, but I don't have further sources to analyze Adam's specific perspective on these issues.