Janelle Nanos of Boston Magazine :
Matt Damon: Robin [Williams]’s best addition is the last line of the film. There was nothing scripted there. He opens the mailbox and reads the note that I had written him. Gus and I were right next to the camera, because every time he came out for a new take I would read the letter to him because it’s a voiceover. He came out saying different lines every single time. When he said, “Son of a bitch stole my line,” I grabbed Gus. It was like a bolt, it was just one of those holy-shit moments where, like, that’s it.
The whole thing is great. Good Will Hunting surely lands in my top 20 list of movies, and maybe in the top 5. This is nice insight into the movie. It’s crazy sometimes to hear how much movies change, or almost don’t get make or change personnel so much before they become the things we love.