There is a complex relationship between the mind and the body. Physical disorders are caused by your state of mind. What you think can literally make you sick or healthy. The attitude you hold about yourself also affects your relationships with other people. Positive thoughts produce positive results, and negative thoughts produce negative results.
Negative people are the product of a negative environment.
Self-talk is what we say to ourselves all day long. A number of sportsmen use this technique to stay positive. Sports psychologists also use it. Some people, on learning that they have cancer, have been known to go into shock and die. There have also been cases of people whom, expected to die far sooner by their doctors, have willed themselves to stay alive for an event like the birth of a grandchild.