Do I need to validate my train ticket in Italy?

Only paper regional tickets, and forgetting costs up to €50. If you buy a Regionale ticket at a station machine or counter and get a paper ticket, stamp it in the small green or white machine on the platform before you board. A valid unstamped ticket is treated as no ticket, and the inspector will not be moved by your story. What doesn't need validating: anything with a QR code bought in an app or online, and any high-speed ticket, because those are tied to a named train and seat. When in doubt, stamp it — validating a ticket that didn't need it does no harm.