Suppose Doug decides to borrow the book from the library. Which result would be a cost?
Doug will save some money by not buying the book. Doug will give up the chance to keep the book as long as he wants.
Doug is deciding whether to buy a copy of a book or borrow it from the library. He would like to be able to keep the book as long as he wants, but buying the book would cost money. He could borrow the book for free, but he would have to return it in a few weeks.
Before you decide to do something, it is often helpful to list costs and benefits.
Costs are what you give up or spend when you decide to do something. Costs involve giving up things that you want or need.
Benefits are what you gain or save when you decide to do something. Benefits involve gaining something that you want or need.
This result is a cost. It involves giving up or spending something that Doug wants or needs:
Doug will give up the chance to keep the book as long as he wants.