The original Wall Street Journal article this was probably plagiarized from.
In short, some customers are valuable (generate a lot of orders) others are of negative value (do a lot of returns relative to orders, spend a lot of time complaining to “customer service”). Customers who are of negative value do not get much effort expended to keep them happy — the company WANTS them to shop elsewhere and be some other merchant’s negative-value pain-in-the-butt.
The Pareto principle (also known as the 80/20 rule in action):
The smart side, 20% of your customers create 80% of your business.
On the flip side, 80% of your problems are caused by 20% of your customers.