A classical way of knowing how strong perception can be is when we consider a clinical condition called anorexia nervosa.
An anorexic person has an unwarranted fear of being overweight.So, she decides to chronically restrict energy intake.
Though she is very thin in reality,her perception about herself is that she is fat even when she is in front of a mirror.
No matter what you say to her,you can’t change her perception by telling her she is not obese!
To her,the reality is her perception.
While this is a life threatening condition which necessitates holistic care for the sufferer,it also further explains how human perception can shape the so called ‘reality’.