I don't believe that just because someone believes something, that that makes it so. But there is something to be said for having a positive attitude; especially when God has made a promise.
As much as 77% of everything we think is negative and counterproductive and works against us. People who grow up in an average household hear "No" or are told what they can’t do more than 148,000 times by the time they reach age 18. Result: Unintentional negative programming.
Shad Helmstetter in Homemade, Jan, 1987.