I've seen nearly every artist I ever wanted to see, although for various reasons I've never been able to catch Judas Priest or Ozzy Osbourne live. Those are the ones I could have seen if things had worked out. I even had a ticket for an Ozzy show in the late 80s but I couldn't get to the show for some forgotten reason.

The ones that were impossible for me to have seen, but would have most wanted to see, would be The Beatles and Jimi Hendrix. I was born a couple of years after the Beatles broke up and after Jimi died.