Good Will Hunting (1997)

Will Hunting is a headstrong, working-class genius who is failing the lessons of life. After one too many run-ins with the law, Will's last chance is a psychology professor, who might be the only man who can reach him.

Robin Williams's Improv Magic: The scene where Sean (Robin Williams) talks about his wife's quirky habit of farting when nervous was completely ad-libbed by Williams. Matt Damon's genuine laughter and the camera operator's shaky attempt to contain their amusement were left in the final cut, adding to the scene's heartfelt and humorous impact.
The Fake-Out Sex Scene: To test if studio executives were actually reading their script, Matt Damon and Ben Affleck inserted a random, out-of-nowhere sex scene between Will and Chuckie. Only Harvey Weinstein at Miramax flagged the bizarre scene, proving he had thoroughly read the screenplay and earning their trust.
Skylar's Real-Life Inspiration: The character of Skylar was named after Matt Damon's then-girlfriend, Skylar Satenstein. She was also a medical student, serving as a direct inspiration for the character; however, the couple broke up shortly before filming began.
Casey Affleck's Reluctant Role: Initially, Casey Affleck was meant to film a documentary about the making of the movie. Director Gus Van Sant had to persuade him to take on the role of Morgan, and Casey improvised much of his dialogue. However, in a recent interview, Matt Damon and Ben Affleck stated that Casey Affleck's claim that he was forced to audition for his role in their 1997 film Good Will Hunting is "a bold-face lie".
From Thriller to Drama: The original script for Good Will Hunting was envisioned as a thriller, with Will Hunting's genius being sought after by the FBI. Rob Reiner's production company, Castle Rock, bought the script but demanded rewrites, leading Damon and Affleck to shift the focus to a character study.