Plumbers and Doctors Share a Common Trait
No one wants a plumber who has only fixed a few leaking pipes. And who wants a surgeon who has only performed a few operations? It's the old story that "practice make perfect".
Studies on cataract surgery show that the more surgeons perform this operation the fewer the number of complications. For instance, surgeons who perform 50 to 250 cataract operations annually show a complication rate of one in 125 cases. For those performing more than 1,000 annually the complication rate drops to one in 1000 cases.
I have no statistics on plumbers, but I'd bet the same holds true.