1) Even if the train from Ostia Antica to Rome appears to be heading in the exact opposite direction than it should, you should probably go for it asap instead of waiting until the doors nearly shut on you.
2) If the doors are nearly shutting on you, do not assume that they are configured like US subway doors, which will bounce open upon bodily contact to preserve human life. These Italian doors mean business. In or out, they say (in Italian).
3) This means that if you just barely manage to get in the train car, you will NOT be able to keep the doors open for your friends. Who are now outside the train. While you are inside the train. Which is leaving.
4) Yelling a curse word really loudly, in panic, as the people you obviously meant to remain with stand helplessly on the track while the train rolls away, turns out to be a LAUGH RIOT for people from many nations. (Though the laughter was not of the mean variety, more of the “dude, that sucks” variety.)
5) If you go to the next transfer point on the train and remain there, your friends will find you in the end.
So at least there’s a happy ending!