It's great if I'm tuning a piano or guitar, but horrible if I'm
  shooting for a particular note or rhythm - I *know* when I'm off
  or when something else is 'off' because I can "hear the beats"
  inbetween the notes. But there's a certain amount of beats
  between two notes that are not in sync that is acceptable and is
  "In Tune". That's how Keith knows where he didn't match up to
  the expectations in his head - he's his harshest critic - as all
  creative people are. as, I suspect, all INFPs are. "