The banjo, in my opinion, is a relatively easy instrument to play passably, but an extremely difficult instrument to play well.
One day when I was a young man, I decided to learn to play the banjo. So I went out and bought one, bought a book to go with it, and taught myself to play. I had been performing with a folk group part-time since I was in high school (summer camp circuit and the like), and I already played the guitar and harmonica well and the piano passably, so I figured the banjo would be pretty easy.
And you know what? It was. But only to the point that the sounds emanating from the instrument could be considered "music" rather than "random noise." Beyond that, the intricacies of banjo technique are both complex and subtle -- the kind of technique that requires technical perfection tempered by something akin to soul. It's the "soul" part that makes the banjo sing.
-Rich