The achievement fallacy is a belief that one's happiness in life is determined by their personal achievements and external markers of success, such as awards, promotions, or material possessions. It overlooks other factors like fortune, privilege, and friends that can play a big role in a person's life satisfaction. The achievement fallacy can have a negative impact on one's mental health and overall well-being. It can cause one to overlook positive events and pleasant experiences along the way, as well as the development of negative tendencies such as perfectionism and a fear of failure.