If we produce corn and decide to store to it for 6 months,
What is the opportunity cost ?
Well, if you stick that corn in a storage bin, it is not earning you any interest. It is just sitting there. If I store the corn for six months, I have lost six months of interest that I could have earned had I sold the corn and deposited the proceeds into some sort of financial instrument. The interest forgone, or the opportunity cost, is a true cost of storage that needs to be taken into account.