I don't think analogy debates are helpful in threads for the specific purpose of giving advise to someone who is involved in a dispute.
I've spit the analogy into this new thread, so the original thread can remain factual.
That's not a defence I'm afraid. It's a bit like arguing that you didn't pay for your sandwich at the supermarket because you were in a rush.
That's not the right analogy.
I'm not sure analogies are helpful here? Analogies can be comical but they don't help us with serious debates.
But if you want a
reasonably correct analogy, you'd need to go with something like this...
You can enter
most cafes and consume an item before paying for it, but at some cafes you must pay first.
Passengers will be legitimately boarding trains at
most* stations without having an opportunity to pay for a ticket before boarding (at some stations it depends which company you are travelling with). Even if you do board without first buying a ticket where facilities are available, you will - in many cases - only be charged no more than the fare you would have otherwise paid.
So it's not surprising some people are very surprised when they are asked to pay more than they'd expect. However it is correct and the £20 should have been paid in the first place.
* There are about 2,500 stations, most of which do not have ticket offices. While a significant proportion of these will have ticket machines, there will still people people boarding trains without tickets legitimately from those stations, because no machine accepts all payment methods.