This is a variation of placebo. A placebo is a pill or medication you tke that is inert yet can have a profound effect on you because of what you believe it can do. A hearcebo can have the same effect except it is derived from things that are spoken to you.

I have a good example for you.

An elderly man has been smoking two packs of cigarettes a day for all his adult life. At his regular yearly checkup with his doctor the doctor tells him he has lung cancer and has to quit smoking. These spoken words have a profound effect on the elderly man and he dies less that 60 days later.

One has to wonder how long the man would have lived if the doctor never spoke those words.