*Playing by ear* I hear a song and I go, "I wonder if I could
   play that?"* and I mess around for a few minutes until I'm like,
   "Ok, GOT IT!" Some are tricky for no particular reason.* The
   chord progression for "Radioactive" from Imagine Dragons stumped
   me for a few minutes, as did the chord progression from one of
   the Minecraft songs a few years back. But once it "clicks in" -
   it's like unlocking a door and stepping through.