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Yes! Now we are getting on to the true cost of advanced tickets.

Fines for making mistakes, rebooking fees, rebooking and having to pay a higher fare, lost tickets because sometimes it's just easier to book a new ticket, losing out when unwell etc...

I bet they make a tidy sum from unused advance tickets

(Great Britain specific):

Although worth noting when it's out of your control the railway does have to offer you options. You don't have 100% of the liability.

And if your train is cancelled you're entitled to take the one before/after for example or get a refund

Though they do make this difficult these days