Positive thinking doesn't mean that you ignore life's less pleasant situations. Positive thinking just means that you approach unpleasantness in a more positive and productive way. You think the best is going to happen, not the worst. Positive thinking often starts with self-talk.
Positive thinking is about seeing things from a positive perspective and maintaining a positive, optimistic attitude. Positive psychology is a branch of psychology that studies the effects of optimism, what causes it, and when it is best utilized.