Hollywood has never been a place where one can keep secrets and rumours usually tend to spread more than the truth. There have been decades of rumors about strange habits, unexpected back-stage activities, and incredible choices of some of the largest stars in the industry. Most of these stories seem to be exaggerated but some of them have been proved later on, which makes reality in Hollywood even stranger than fiction is.
Secret Generosity

Years on, individuals near film sets discreetly alleged that Keanu Reeves habitually gave away a good part of his income to employees who operated in the background. The account proved too good to pass as true until other employees verified that on the occasion of The Matrix movies he handed millions of his bonus money to stunt crews and special effects men who assisted in making the action in the movie real.
Extreme Stunts

It was rumored, more often than not, that Tom Cruise insisted on doing his own high risk action scenes when studios were advocating less risky ones. The reality was unveiled when the videos and accounts of production exposed that he himself acted in numerous of the strenuous stunts in the Mission: Impossible series, such as climbing high buildings and artistic aerial moves.
Hidden Cuecards

Years of stories went round that Marlon Brando liked working with cue cards rather than memorizing a script. Later on, film crews attested that he had dialogue occasionally put around the set or even written on objects so that he could deliver his performance in a more natural way and not have to memorize lines of long passages so rigidly.
Method Commitment

It was believed that Daniel Day Lewis was in character during whole productions including after the cameras were off. The later confirmation of actors and crew members attested to the fact that in some projects he would remain speaking and acting the part for weeks or months and his acting was very authentic.
Joker Preparation

Heath Ledger had initially heard rumors that he spent weeks in isolation preparing to play the Joker before the release of the Dark Knight. Following the success of the film, some information surfaced that he did have a secret notebook in forming the voice, mannerism, and disturbing personality of the character.
Script Doctor

There were industry rumors long to the effect that Carrie Fisher secretly assisted in the bettering of movie scripts with much of the time going unacknowledged. Filmmakers over the years recognized that she was frequently brought in to refine dialogue and reinforce scenes and she was respected as a talented and reliable writer in the background.
Practical Effects

Most viewers thought that the director, Christopher Nolan, favored the real-world approach to filmmaking instead of excessive dependence on computer-generated effects. Later production reports have verified that he often employs real sets, physical stunts and huge scale of realistic visuals to give the immersive worlds that are experienced in films such as Inception and the Dark Knight trilogy.
Improvised Line

One of the most renowned movie scenes was even said to be unscripted as the filming took place. Later on, Harrison Ford admitted that his nonchalant reply of I know in The Empire Strikes Back was actually an improvisation that substituted the initial one and would end up happening to be one of the most significant moments in the whole saga.