Looking at fragments alone, it's hard to glimpse the whole picture.
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history
From 世说新语·方正 - a young 王献之 watched players over their shoulders and was scolded: 管中窥豹，时见一斑 (gazing at a leopard through a tube, one only sees a single spot). 全豹 ('the whole leopard') is the contrast - seeing the entire animal, the complete picture.
usage
Almost always appears in the patterns 难窥全豹 (hard to see the whole), 略见全豹 (catch a partial glimpse of the whole), or paired with 一斑 (one spot) for explicit contrast.
