A sudden realization or awakening to the truth; when something becomes clear and one is impressed or enlightened (lit. 'scales fall from one's eyes').
彼の説明を聞いて、目からウロコが落ちた気がした。
After hearing his explanation, I felt as if scales had fallen from my eyes.
使い方のコツを教えてもらって、目からウロコだった。
I was taught a usage trick and it was a real eye-opener.
その事実を知って、目からウロコの思いがした。
Learning that fact made me see things in a new light.
講義の一節がまさに目からウロコで、研究の方向が変わった。
A passage in the lecture was truly eye-opening and changed the direction of my research.