In the US, when we travel on the airplane, we regard the boarding pass as disposable. Lost it? It can be reprinted.
This is NOT the case with the boarding pass for a train. We purchased a cabin for the night train from Split to Zagreb. I ran quickly to send an email at a nearby cafe, and somehow dropped the pass at 10 PM. We were forced to re-purchase our cabin. Of course, as my wife noted, only an idiot would drop the pass. Nonetheless, it is a warning for others.