the scales fall from sb's eyes

said to mean that someone suddenly realizes the truth about something after a long period of not understanding it or of being deceived about it

指某人在很长一段时间不了解某件事或者被骗了之后，突然意识到这件事的真相

The scales have finally fallen from his eyes and he realises that he's made a dreadful mistake.

他终于醒悟过来，意识到自己犯了一个可怕的错误。