Completely agree. There was an experiment on this. A prisoner was to be sentenced to death. He was told to be injected with the poison. A fluid was injected and his blood was observed in lab in terms of changes. It was noticed that the he was unconscious due to the poison but in fact the injected fluid was nothing more than water. As he assumed that it will be poison, so the water acted like poison. It's lot more about the way of thinking.