To know only one aspect of a thing but not the whole picture; to have a partial or one-sided understanding.
很多人在评价他人时，往往只看到表面的缺点，知其一未睹其二，无法全面客观地看待问题。
When evaluating others, many people often only see superficial shortcomings, having a partial understanding and failing to see the whole picture.
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