Pithy, but you're misunderstanding the application of that principle.The Pareto Principle in business states, 10 percent of your customers provide 90 percent of your profit. the other 90 percent of your customers spend lots of money but in small amounts. Smart companies always cater to the 10 percent first then the 90 percent.
You don't respond to "show me who the people buying books are" with "cater to the people buying books". The question being asked is WHO are those people. You haven't answered that.