They know what they're driving: a train.
Contrary to say driving a truck or a car, the length of the vehicle doesn't change it's behaviour. So it's really easy for a driver to hop on a 8-coach train and drive it like a 6-coach train without feeling there's more behind him - maybe his train is normally a 6-coach vehicle, but as the normal train is in maintenance, they used an 8-coach one this time. With a truck you feel whether you're laden or not, whether you have that second trailer attached or not.
Once I've seen a train arriving in the station, with two engines, the second of which producing massive amounts of smoke. The train conductor went upfront to warn the driver of this, the driver, operating the train manually, hadn't noticed anything - the conductor noticed the smell of the burning brakes. What happened: the brakes of the second (inactive) engine were locked, and for the past 12 km or so the train had been pulling not only the 6 or 8 coaches, but also an engine with the brakes full on. The smoking hot brakes were released, and with a few minutes delay the train continued its journey.
The solution of having them pull up to the far end, is of course a failsafe option, while also being clear to passengers on where to expect the train to stop. Having the length of their train written somewhere in the cab as reminder may also be a good idea.