Beliefs vs. Reality

If we are wrong when we argue with reality 100% of the time, how can we create a believable new positive belief that is based on how we want to see “our future selves” that is actually very different from our current negative reality? Or put another way, knowing that we can choose to believe whatever it is the we want to believe, can we really choose to believe something about ourselves that we know doesn’t jive with our current reality?