An economist remarks that the cost of consuming a book is the combination of the retail price

Question:

An economist remarks that "the cost of consuming a book is the combination of the retail price and the of the time spent reading." Isn't the cost of consuming a book just the price you pay to buy the book? Why include the cost of the time spent reading the book in the cost of consuming the book?
Opportunity Cost
Opportunity cost is the profit lost when one alternative is selected over another. The Opportunity Cost refers to the expected returns from the second best alternative use of resources that are foregone due to the scarcity of resources such as land,...