《淮南子·人间训》
如果在霜降以后再种谷子，到来年冰化时就想收获，这样来求粮食就难了。所以《易经》上说： 潜龙勿用。 
今霜降而树谷，冰泮而求获，欲其食则难矣。
If you plant rice after the frost, and you want to harvest it when the ice melts next year, then it will be difficult to get food. Therefore, the Book of Changes says: "Hidden dragon, do not use it."