In message , David
Cantrell writes

They're clearly capable of learning, but it's not made obvious that
there is anything to learn in the first place. It certainly *appears*
to work the same way as the tube - slap your wallet on the yellow thing
and usually the barriers open (but at other times you need to do it
several times) just like at tube stations.

Except that the majority of NR stations don't have barriers.

It may be more useful to think in terms of what happens with paper
tickets. Your Zones 1-2 travelcard will appear to work fine for a
journey from Waterloo to Mortlake - it will let you in at Waterloo and
there are no barriers at Mortlake to prevent you leaving the system. But
if you haven't learned that you need to buy an extension ticket to
travel beyond Zone 2 you risk a Penalty Fare if gripped beyond Zone 2.
--
Paul Terry