I certainly agree that positive thinking is the key to success in life. Being able to handle difficult issues or disasters in a positive way is a sign of personality strength and is allied to other advantageous traits such as determination and willpower

Having said that many intelligent people suffer from self doubt at one time or another. Even the great Winston Churchill did apparently but his inner strength of resolution overcame this. I believe it is a matter of getting things into perspective when things go wrong in your life. It rarely turns out to be as bad as you first thought.

Certainly the mind has power over the body and positive thinking, i.e. optimism, helps enomously when combatting serious illness such as cancer.

I don't know whether the predominance of optimism is genetic but it doesnm't hurt to believe that you can train your mind to think more optimistically - Hey let's do it!