Every studio wants a card-carrying A-lister to headline their new project, because even though many believe the age of the movie star is over, audiences are far more likely to turn up for a film starring one of their faves, right?
Yet, sometimes a movie star simply can't see the wood for the trees and appreciate that, no matter how famous and popular they might be, they're not necessarily right for a specific role.
No matter how talented and beloved a performer may be, nobody is a perfect fit for every part offered their way, and it takes a major absence of ego for them to realise they're better off passing on a project.
But inspired by a recent Reddit thread on the subject, these 10 actors - all of them male, curiously - ended up ruining movies through their sheer involvement.
Perhaps their ego-centric need to control the production steamrolled the creative aspect, or maybe things changed hugely behind-the-scenes once their name was attached.
Whatever the reason, and whether it was actively their fault or not, these actors were all responsible for these movies becoming demonstrably worse...
10. Will Smith - I, Robot
Alex Proyas' 2004 blockbuster I, Robot started out life as an original script from Jeff Vintar called Hardwired - an Agatha Christie-esque murder mystery in which an FBI agent investigates the murder of a roboticist, with the entire movie being set at the scene of the crime.
The project passed through the hands of numerous actors, including Arnold Schwarzenegger and Denzel Washington, before Will Smith finally became attached.
But with Smith's involvement, Fox began to envision the story as something much grander, and so writer Vintar was brought back to expand it into an action-blockbuster worthy of a $120 million budget.
Oscar-winning writer Akiva Goldsman (A Beautiful Mind) was also hired to polish the script for Smith, all of this ensuring that Vintar's modest original concept was basically tossed out for a broader, more schlocky sci-fi action tentpole.
Simply, Smith's involvement mutated the entire project beyond its writer's original intent, because there was no way either Fox or Smith were going to sign off on a sci-fi chamber piece.
While the end result isn't terrible, it is a bastardisation of both the original concept and also Isaac Asimov's work that inspired it, to which it ultimately bears only the vaguest resemblance.