Two different systems that look like one, and a boarding time that is not the departure time.
High-speed trains are not the same product as regional trains
Italy runs two things from the same stations, and the difference is not comfort. It is whether your ticket is tied to a specific train.
High speed — Frecce and Italo
Reservation is compulsory and the seat is assigned. Your confirmation shows a coach and a seat number.
It does not show a platform. The platform is published on the departure boards shortly before the train leaves — often only ten or fifteen minutes before. This surprises people who expect it printed on the ticket, and it is the reason to be in the station early rather than on the platform early.
Nothing to validate. The ticket is tied to that train on that day.
Prices behave like airline prices: they rise as the date approaches, and the cheapest fares are non-refundable.
Regional trains — and the one that gets fined
No seat assignment, and generally valid for a time window rather than a single train.
A paper regional ticket must be validated before you board, in the small machine on the platform or at the entrance to the platforms. An unvalidated ticket is treated as no ticket, and the penalty falls on tourists more than anyone else because nobody tells them.
If you buy through an app and travel on a digital ticket, validation generally does not apply — but the paper one you bought at a machine does need it. When in doubt, validate.
Strikes are frequent, announced, and survivable
Transport strikes in Italy are common and are declared days in advance. They affect trains, flights, buses and city transport, sometimes more than once in the same month. During a rail strike a set of guaranteed services still runs.
The practical consequence is narrow: a strike on a day you are sightseeing is an inconvenience, and a strike on a day you move between two cities is a broken trip. Check the dates against your transfer days, not against your whole holiday, and keep the transfer days flexible if you can.
Ferries: the time on the confirmation is not the departure
If you are taking a car to Sardinia, Sicily or the smaller islands, read the confirmation carefully. It gives a reporting time at the boarding gate, and that time is significantly earlier than the departure time — commonly by a wide margin for vehicle loading.
Put the boarding time in your plan, not the departure time
Vehicle loading closes well before the ship leaves. Arriving between the two means watching your ferry depart with your booking on it. Work backwards from the reporting time when you plan the drive to the port, and add margin: this is the one deadline of an Italian trip that does not wait.
Sources: booking confirmations from Italian and Adriatic ferry operators; Trenitalia and Italo ticket conditions.