Mǎi guā kàn pí; mǎi zhēn kàn kǒng.

買瓜看皮, 買針看孔。

Lit [When] buying melons, look at [their] skins; [when] buying needles, look at [their eye-]holes.

Fig One must focus on the key points in making observations.

Topics KEY POINTS OBSERVATIONS PROBLEMS