(The alert reader will notice that it says “Mediation” instead of “Meditation”. I dont know why, but I know who to ask, and I will.)
People have, somewhat justifiably jumped on this error message, complaining about how terse it is, for instance Max Rozen who makes some good and sensible suggestions about good and sensible error messages.
But all his suggestions require some amount of ambient information, information which we in the Varnish Cache project do not have and never can have.
When Varnish gets to the bottom of the builtin.vcl and errors out, we dont know where that Varnish instance runs, who it runs for, what information it serves, who it serves that information to and most crucially, what information can safely be shared with the clients.
This is why the default “503 guru meditation” only mentions the XID: The XID is a nonce, for all practical purposes a random number, but one which allows the persons responsible for that varnish instance to dig through their logs and find out what happened to this specific request.