This document discusses the lifetime value of customers and how marketers can maximize it. It notes that according to the 80-20 rule, 80% of company profits typically come from 20% of customers. It defines a profitable customer as someone who generates more revenue than costs over time. It also discusses calculating customer lifetime value, which is the net present value of expected future profits from a customer over their lifetime with the company. Key factors in the calculation include price paid, direct servicing costs, discount rate, probability of repeat purchases, and acquisition costs.