In 2014, after Robin Williams died, the bench in the Boston Public Garden where he and Matt Damon had their conversation scene became an impromptu memorial site. People left flowers, quotes, and various items at the bench. A petition has been passed around to erect a statue in Williams' memory near the bench.
On the first day of the shooting, Matt Damon and Ben Affleck started crying out of happiness, because it was a scene between Robin Williams and Stellan Skarsgård, accomplished actors, doing Damon's and Affleck's scene verbatim, and they had waited five years for it to happen.
Matt Damon and Ben Affleck found a clever way to choose the right studio for their script. The story goes that on page 60 of the script, they wrote a completely out-of-nowhere sex scene between Sean and Lambeau. They took it to every major studio, and nobody even mentioned the scene. When they met with Harvey Weinstein at Miramax, he said, "I only have one really big note on the script. About page 60, the two professors, both straight men, have a sex scene. What the hell is that?" Damon and Affleck explained that they put that scene specifically in the script to show them who actually read the script and who didn't. As Weinstein was the only person who brought it up, Miramax was the studio chosen to produce the film.
The lines in the scene when Sean talks about his late wife's farting antics were ad-libbed by Robin Williams. That is why Matt Damon was laughing so hard. If you watch the scene carefully, you can notice the camera shaking a bit, possibly due to the cameraman laughing as well.
When Matt Damon was in his fifth year at Harvard, he was in a playwriting class. The culmination of it was to write a one-act play. He started writing a movie, which with the help of Ben Affleck became this movie.