Some semi-spoilers mixed in…
There’s a lot of imagery in this movie especially revolving around trains which is an easy tie in. Fin is very much like a train: he dresses ‘old fashion’ and in black, he smokes, walks train tracks, doesn’t speak hardly at all, very isolated, alone, no emotion or desire for interaction, etc.
He’s content to live in solitude and even desires it. However, Joe, by his nature, insists on becoming his friend. His life is marked by service and human contact: he works a hot dog/ice cream/coffee stand and does that to serve his father (he’s serving to serve). He forces his way into Fin’s life and forces Olivia to come along to.
Olivia creates and nurtures but her life is a (train) wreck. She wants to help and it seems to provide for Fin in a way she can’t for her son who died a couple years before. She sees Fin as someone to fill this role in her life as her son.
Joe’s excitement and Olivia’s motherliness eventually brings Fin out of his shell and converts him from a ‘train watcher’ to a ‘people watcher.’ He starts wearing clothes w/ some color, being interested in others and eventually smiles and cracks a joke.
He opens up only to find he gets hurt like he always feared. The resolution is not overwhelming or overly sappy, but well done and simple.
The acting is spot-on and the characters come thru instantly even if you don’t know it at the time.