目を疑う。

The phrase combines 目 (me), meaning 'eye,' and 疑う (utagau), meaning 'to doubt' or 'to suspect.' Therefore, literally translated, it means 'to doubt one's eyes.' This idiom has been in use for centuries in Japan to express extreme disbelief or astonishment at something one witnesses. While a precise 'origin story' for this exact phrasing is difficult to pinpoint to a single event or author, its construction follows a very common pattern in Japanese where a noun (目 - eye) is combined with a verb (疑う - to doubt) to form an idiomatic expression describing a state or action related to that noun. Many similar expressions exist in Japanese, and indeed in other languages, where sensory organs are paired with verbs of disbelief or surprise to convey a similar meaning (e.g., 'I can't believe my ears,' or 'it was an optical illusion'). The phrase is rooted in the fundamental human experience of encountering something so unexpected or extraordinary that it challenges one's perception of reality. It's a testament to the idea that sometimes what we see can be so startling that our minds instinctively question its veracity. Its continued use reflects its effectiveness in conveying a strong sense of disbelief. Over time, its meaning has solidified to represent a state of profound shock or astonishment upon witnessing something truly incredible or improbable.