He has the delusion that he can become a professional basketball player without ever practicing.

delusion 是名词，来自动词 delude（欺骗、迷惑），前缀 de- 表示"偏离"，词根 -lude 与"游戏、欺骗"相关。delusion 指"错误的信念或幻想"，通常指与现实不符的固执想法。