Here you buy a ticket, get on the train, the ticket inspector checks that it is valid for your journey, lets assume it's an standard open single so can be used on any train, once you are on the train you are making the journey so are deemed to have used the ticket, so the inspector punches your ticket and from that point on it's dead, after you journey put it in the bin, you can't use it again on any other train.
I'm going to Lille by Eurostar on Saturday and then onwards from Lille by TER. My wife tells me "don't forget to stamp your ticket in the machine before you get on the train", what
?? If I buy a ticket at the ticket desk and immediately proceed to the machine to stamp it myself before I get on the train, how the hell does the conductor know how many trains I've been on using that ticket? It's like stamping your own stamps before you put the letter in the letterbox, you could use the same stamp 100 times.
My wife can't explain to me why, but can only tell me that I have to stamp the ticket. There must be some logic I'm missing here, can anybody fill me in? Does it stamp a date and time then invalidate if you haven't caught a train within the next hour or something?