Considering that actors are often the most famous names associated with a given project, they're right up there with the directors, producers and writers of a film in terms of how much pressure they have on their shoulders.
And just like everyone else involved in the creative process, the stars can bring their own ideas and quirks to the table, resulting in a lot of possible avenues down which to take each individual scene. But not all of these avenues are made of solid gold.
In fact, because of how unpredictable and difficult movie-making can be, some actors have even come close to ruining an important scene, whether by contributing an idea that sounds like it would've been terrible, spoiling a strong take with a poorly timed reaction, or simply by being reluctant (or unable) to perform an important moment.
Fortunately, these sequences turned out great in the end, but their magic could've been diminished - or even vanquished entirely - if the actors' odd behaviour, wild ideas or bad on-set conduct had been allowed to influence the final outcome of the scene.
10. I'll Be Back (The Terminator)
"I'll be back" isn't just one of Arnold Schwarzenegger's most iconic quotes - it's one of the most famous lines in the entirety of cinema, and has been repeated ad-nauseam ever since it was first uttered in 1984's The Terminator.
However, if the actor had got his way, then movie history might not have remembered the scene as fondly as it does today.
Spoken by the T-800 right before it decimates a police station full of helpless cops, Schwarzenegger and director James Cameron initially disagreed on exactly how the line should be spoken, with the filmmaker preferring the more contracted "I'll be back", and the actor favouring the more drawn-out "I will be back".
Schwarzenegger's reasoning was that the line sounded more machine-like without the contraction (plus, with his thick Austrian accent, he had difficulty pronouncing "I'll"), which is actually fair of him to point out, because the Terminator doesn't typically use shortcuts when speaking. But when Cameron told him to just read what was in the script, the actor relented, delivering a major piece of pop-culture history in the process.
Had Arnie won the argument, the scene would've lost that touch of magic, and possibly wouldn't have been quoted over and over again by fans in the decades since.