Positive thinking is a mental attitude that allows into the brain thoughts, words and pictures that are conductive to evolution, expansion and success.
It's a mental attitude that anticipates great and favorable results. A positive mind anticipates happiness, joy, health and a successful result of every situation and action. Whatsoever the brain expects, it finds.
Our current mental attitudes are habits, put together from the feedback of parents, friends, society and self, that forms our selfimage and our world-image.
These attitudes are maintained by the interior conversations we constantly have with ourselves, both consciously and subconsciously.