It can seem like Hollywood is all glitz and glamour, but while the idea of being famous is appealing to many of us, a lot of real, hard work goes into movies behind the scenes. That work can test a person’s limits not just as an actor but as a human being.

Lauren Cohan in the Walking Dead

The Walking Dead nearly suffered what would have been a devastating loss in Season 3, when Lauren Cohan, who plays Maggie, contemplated quitting over a particularly stressful scene.

After reading the script and realizing Maggie was supposed to perform an emergency c-section on another character, she took her concerns to co-star Steven Yeun, explaining she was worried it would be too intense—yet after further consideration, that’s exactly why she decided to stay.

Recognizing that TWD is a show about people pushed to grueling extremes, she drew on her discomfort to deliver an affectingly honest performance.

Ian McKellen in The Hobbit: An Unexpected Journey

It’s almost impossible to imagine the role of Gandalf being played by anyone other than Sir Ian McKellen, who put his indelible stamp on the character in all six Lord of the Rings and Hobbit films.

But if things had worked out a little differently during the filming of The Hobbit: An Unexpected Journey, director Peter Jackson might have had to find a different actor for the part.

The problem? McKellen was acting almost exclusively to a green screen, owing to the fact that his character towered over the hobbits and their interactions had to be stitched together digitally in production.

The frustration of acting alone eventually got to McKellen, who broke down on the set at one point, but Jackson did a little emergency outreach to convince him to stick around.

Al Pacino in The Godfather

Al Pacino earned a Best Supporting Actor Oscar nomination for his work as Michael Corleone in The Godfather and a Best Actor nomination for the sequel, so it’s laughable to think studio execs initially wanted him removed from the role—yet according to Pacino, that’s exactly what happened.

He felt resistance so acutely, in fact, that he later claimed he would have walked off the set if director Francis Ford Coppola hadn’t been so supportive during those early days on the Godfather shoot.