《淮南子·说林训》
毛色驳杂的豹皮大衣不若毛色纯一的狐裘大衣；白璧有了污点裂缝，就不能变宝贝了：这是说绝对纯粹是困难的。
豹裘而杂，不若狐裘之粹；白壁有考，不得为宝；言至纯之难也。
A leopard skin coat with mixed colors is not as good as a fox fur coat with a pure color; a white jade with stains and cracks cannot be a treasure: this means that it is difficult to be absolutely pure.