Of course, naming is one of the "Two Hard Things".

It's absolutely an art, not a science. But it shouldn't go to either extreme -- names that are too short (var xi_a) are too confusing for clarity, but names that are too long provide too much visual noise to be clear.

In my opinion, "make_person_an_outside_subscriber_if_all_accesses_revoked" just takes too long to read. Much better would be something like this:

  // If all accesses have been revoked, then make the person an outside subscriber

  def updateOutsideSubscriber
    ...
  end

The function name is short and gets straight to the point of what it does. Someone coming across the code for the first time can instantly figure out roughly what the function is, and then decide if it's worth their time to read further, or if they should just skip over it.

Then, a comment explains in further detail what it is for, and why it is used. You only need to read it if it seems important to your task at hand.

Good variable naming strategy goes hand-in-hand with good commenting strategy.

The end goal should always be maximum clarity, but remember that too much information, or too much information presented upfront, can reduce clarity.

37signals says "clarity over brevity". I'd say "clarity over extremes".