6 O Finance and investment 123 employees earn less than £20,000 a year; if you make comparisons by looking at which percentile a person is in, suggesting that the difference between the salary of the person in the ninety-fourth percentile and the one in the eighty-ninth is similar to the difference between those in the fifty-fourth and forty-ninth percentiles would be quite wrong. Percentiles just tell you about the order of things, not about the amount of difference between them. Real-life stories Y oujustcan'treasonwithsomepeople As anyone who deals with customers knows, there are some people who just won't listen to reason. This often occurs in the investment world. We should have a little sympathy for the stockbrokers and financial advisers who sometimes have to deal with loopy investors who have mad theories about how investment works and won't be persuaded otherwise. There have always been people who ignore mathematical proofs, and there always will be. Take the problem of squaring a circle. It can be proved that it is impossible geometrically to construct a square that has exactly the same area as a given circle. This proof has not deterred circle-squarers, however, who continue to try to show that it can be done.