Whether there were ghosts in the world was a controversial topic. There was currently no conclusive scientific evidence to prove the existence of ghosts or supernatural phenomena. However, some people may claim to have experienced supernatural events such as seeing ghosts, supernatural phenomena, or being haunted by ghosts. These experiences may be related to personal psychological effects, beliefs, life experiences, and other factors. Some people might have a perception of supernatural phenomena due to individual differences such as the perception of their eyes, the structure of their nervous system, and so on. These perceptions might not be facts, but they could also be subjective misunderstandings or illusions. For students who always see those unclean things, this may be related to personal life experiences, psychological state, environment, and other factors. For example, some people might encounter something unclean in certain scenes or experience some negative life events, resulting in a negative psychological reaction. It is recommended to seek professional psychological consultation or help to better deal with these problems.