illusion 錯覺（正常人判斷錯誤）: Something that is false or not real but that seems to be true or real, e.g.,
The video game is designed to give the illusion that you are in control of an airplane.
hallucination 幻覺（被影響的正常人）: an experience in which you see, hear, feel, or smell something that does not exist, usually because you are ill or have taken a drug, e.g. A high temperature can cause hallucinations.
delusion 妄想（指瘋子的想法）: A delusion is a fixed belief that is not amenable to change in light of conflicting evidence, e.g., she is under the delusion that we will finish on time.