You are trying to decide whether to take a vacation. Most of the costs of the vacation (airfare, hotel, and forgone wages) are measured in dollars, but the benefits of the vacation are psychological. How can you compare the benefits to the costs?
The benefits of a vacation will vary from person to person. Most people associate a vacation with relaxation, peace and a chance to spend quality time with family. If a person feels they need these psychological benefits then the costs of a vacation may be worth it. When you spend money for pleasure the cost question is not counted because here the cost has no value as this money is spent for your pleasure which is a psychological matter and hence comparing the cost to Benefits never arise here. At the maximum you can say is that it is an opportunity cost for you and if the vacation gives you more psychological benefits then we can say the cost is cheaper compared to the benefits.