The psychologist’s fallacy is a term coined by the Psychologist William James. It simple language it refers to when one is assuming incorrectly to know what someone else is experiencing. When you go to a friend for help with a psychological problem they will often try to relate your experience to an experience they had. This is not helpful because they did not take the time to really understand your problem first. Another approach they may take is to offer advice.
A good therapist will seek to understand your unique dilemna. They will help you find a solution for yourself.