Well, therapy is an art. Knowledge is required, but also skill, finesse, timing, experience, sensitivity, and raw talent.
There are plenty of people who have played the piano for many years, but how many Rubensteins or Van Cliburns are there?
Or translate that to a sports metaphor, if that makes more sense: there are many basketball/baseball/football players, but how many [insert name of star player here] are there?
Most people in their jobs are just average. That's why they call it "average."
