The system can be a bit of a minefield, though, and as we have seen in this section of the forum, there are many cases where someone has fallen foul of the rules due to making a fairly basic mistake. I recall one recent case where someone boarded at a station with no ticketing facilities, no reasonable opportunity to purchase en route, and alighted at another station without facilities and subsequently ended up in trouble.
There's no consistency across the network. Until I joined the forum, I was under the impression that it was perfectly okay to get on a train and pay the conductor. Indeed, I could probably make a local journey today and have the conductor sell me a ticket on board. I know now to make sure I use the TVM or visit the ticket office, but hitherto it was considered perfectly acceptable to buy on board. Not once have I been advised by a conductor that this isn't the correct behaviour, and there's no real incentive for them to do so if they're earning commission from the sale.
If I decided to have a holiday in, say, Northernland and boarded a train expecting the situation to be the same, I'd be in for a shock. Your average punter won't be versed in the finer details of the Conditions of Travel.
There are a few forum members who will tut and shake their heads and seem to be of the "yeah, yeah, we've heard it all before" mentality, but generally I find that those giving advice do so in a sympathetic manner and recognise that we're human and occasionally prone to the odd blunder.