UPDATE: Oops, I tried a shortcut that didn't work. Here is the opening of the violin part. All open strings:
Berg famously opens with just the open strings of the violin. I guess I should take a lesson in how to hold the bow first. If you asked me to play the rest of the concerto, though, not in a million years!
You see, it is not instruments that are hard or easy to play, it is the music written for them. There are a very few instruments that have proven to be so useful and so expressive and so capable that composers have chosen them over and over again, to use for the most challenging and expressive music. There are a zillion great violin concertos because the violin is an astonishingly capable instrument. What this means is that if you want to be a violinist, capable of playing this virtuosic repertoire, you need to start quite young (seven at the very latest), you need to have loads of musical potential, you need a wonderful teacher, you need a wonderful violin and you need to work very, very hard for a decade or two. And at the end of that time you might be able to do a good job playing the Berg violin concerto or the Tchaikovsky, or the Beethoven.
Instruments like the violin, the piano, the cello, even the guitar, are very difficult to master, not because of any characteristics of the instruments themselves, but because of the kind of music that has been written for them. Mind you, to play any orchestral instrument up to the standards of a professional orchestra is also pretty tough--just not quite as demanding as being a soloist.
Things in the pop world work a bit differently. Not to say that instrumental virtuosity isn't also part of the scene, but it does not dominate in the way it does in the classical world. A great pop vocalist is probably as much a great vocalist as is an opera singer, but the technical demands are quite different. A great guitar virtuoso like Eric Clapton is probably playing on a level of mastery that is the equal of nearly any classical musician. But you can't say the same of the rhythm guitarist in a reggae band who is destined to play pretty much the same rhythms his whole career.
Some instruments you might think are nothing to play, like the blues harp. But in the hands of a true master, you start to see that if you want to do what he can do, it will take a lot of work. But just about anyone can get some kind of tune out of a blues harp! Some instruments are easy to pick up and fool around on. I learned how to play the African thumb piano (mbira) well enough to play my part in a contemporary piece--but the part was simple.
Let's end by listening to the first movement of that violin concerto by Alban Berg: