"There is an old saying that fugues are the type of music in which the voices come in one by one while the audience goes out one by one, but there is no statistical evidence to support this; audiences have been known to leave in droves."
What fascinates me about this joke or other jokes as well is that you have to hold your mind open while you're listening to it. A punchline happens only at the very end.
Although this is a short joke, still, you have to be patient, suspend disbelieve and actually trust that in the end it will all come somehow together.
The ending is strangely surprising and at the same time satisfying. Don't you feel satisfied by this joke? I do.
I feel satisfied because I remember some of the times in my recitals when fugues were the hardest pieces for the audience to feel a connection to. Every organist who has ever played a fugue in public will know this.
That's why jokes have to be empathetic in order to be appreciated.
Likewise, when you're improvising, you feel kind of that way too - you trust that it sounds surprising to people and never shake your head and say: "No, this is a bad improvisation. I don't like it and people will leave before I finish (like in this joke)."
Actually, you also hope that it will all come together in a satisfying way to yourself and to the people around you.
Improvisation requires curiosity.
PS In addition to the 6 variations that are already composed, I've been asked to create also the Toccata as the 7th variation for the cycle on the hymn tune "O Master, Let Me Walk With Thee". I'm starting to work on it and teach how to create it for my Modern Variation Workshop.