If your instrument is a huge one, sure, most of those folks have just one, but I think you underestimate the number of instruments that some orchestra folks have. A lot of folks have "traveling" instruments - if they're going on a plane, they don't bring the really good one. In High School, I had two violins - a really nice, 100 year old one, and the really good (but not stellar) one. I had a few High School friends that also had 2 or more instruments back then. If High schoolers have more than one....