The idiom 一目了然 literally means 'one glance, completely clear' — it describes something so immediately obvious or transparent that no further explanation or analysis is needed. Each character contributes to this meaning: 一 (one), 目 (eye/glance), 了 (to complete/understand fully), and 然 (thus, in this state). Together, they evoke the image of instantly grasping a situation upon first seeing it.

This expression is commonly used in both spoken and written Chinese to describe visual clarity, logical simplicity, or intuitive understanding — for example, when a chart, layout, instruction, or problem’s solution is self-evident. It carries a slightly formal but neutral tone, often appearing in academic, professional, or descriptive contexts. While not limited to visuals, its origin lies in sight-based comprehension, so it’s especially fitting for anything perceived directly and effortlessly.