《淮南子·俶真训》
严寒来临，霜雪铺地，这才能看出松柏的茂盛不凋；处境困难，面临危险，利害关系呈现眼前，这才能看出圣人不弃 道 的本性。
夫大寒至，霜雪降，然后知松柏之茂也；据难履危，利害陈于前，然后知圣人之不失道也。
When severe cold comes, frost and snow cover the ground, then one can see the flourishing and unfading of the pine and cypress; when one is in a difficult situation, facing danger, advantages and disadvantages appear before one's eyes, then one can see the Saint's essential nature of not abandoning the Tao.