If a movie is an absolute stinker it usually goes straight to DVD or gets released online.
But some films were so dodgy they never saw the light of day.
Here are three films you probably never knew existed:
A Fantastic Four movie was filmed in 1992 and was set to be released in 1993. But it magically disappeared and was never shown on the big screen.
So who is to blame?
According to Stan Lee, that would be a German producer named Bernd Eichinger.
"That movie was never supposed to be shown to anybody," Lee told Los Angeles magazine.
"The fellow [Eichinger] had the rights to do the Fantastic Four movie for, like, 15 years, and finally the option was due to lapse. If he hadn't begun principal photography by December , he would lose that option."
If Eichinger did make a Fantastic Four movie though, he'd get to retain his rights to the characters.
"So he figured he would bat out a fast movie for a $1.98 budget just so he could keep that option," Lee said.
"The tragic thing is that the people involved with the film were not aware that that movie was never supposed to be seen by any living human beings."
Now it should be noted that Eichinger disagrees with Stan Lee and maintains he wanted to release the movie.
"It was not our intention to make a B movie, that's for sure, but when the movie was there, we wanted to release it."
Instead, Eichinger told the magazine that he sold the only copy of the finished movie to a Marvel executive who wasn't impressed with the shoddily-made film.
"He [Avi Arad] really didn't like the idea that a small movie was coming out and maybe ruining the franchise."
In 2002, Arad confirmed that he bought the movie for "a couple million dollars" and said he burned it.
FYI - the movie has since surfaced online and has been posted on YouTube, so he clearly didn't burn the only copy.
As for Eichinger, he went on to produce a big-budget version of Fantastic Four starring Jessica Alba and Chris Evans in 2005 and followed it two years later with Fantastic Four: Rise of the Silver Surfer.
The Day The Clown Cried
In 1971, comedian Jerry Lewis wrote, directed and starred in a movie called The Day The Clown Cried.
But it was so bad that Lewis himself banned it from ever being released.
"I was embarrassed," the legendary entertainer said about the film in 2013.
"I was ashamed of the work and I was grateful that I had the power to contain it all and never let anybody see it. It was bad, bad, bad."
So what's the movie about? Strap yourself in, it's a doozy.
In the film, Lewis plays a German clown named Helmut Doork who is sent to a WWII prison camp after mocking Hitler in public.
Once inside he ends up performing for Jewish kids who are also imprisoned and ultimately ends up trying to keep them entertained as he guides them into the gas chambers at Auschwitz.
One of the only people to have seen the finished product apart from Lewis is Simpsons star, Harry Shearer, who wrote about the film in Spy magazine in 1992:
"With most of these kinds of things, you find that the anticipation, or the concept, is better than the thing itself. But seeing this film was really awe-inspiring, in that you are rarely in the presence of a perfect object. This was a perfect object.
"This movie is so drastically wrong, its pathos and its comedy are so wildly misplaced, that you could not, in your fantasy of what it might be like, improve on what it really is. 'Oh My God!' - that's all you can say."
Jerry Lewis has said "it'll never be seen" but in 2015 it was revealed the star sold a copy to the Library of Congress and has given permission for it to be screened in 2025.
For more than 20 years, Leonardo DiCaprio and Tobey Maguire have been trying to block Don's Plum from being released.
In the black and white indie film, which was shot in 1995/96, the two actors play teenagers who meet up at a local diner to discuss their lives.
Their characters aren't very pleasant and apparently the two stars improvised most of their lines.
In one scene DiCaprio's character says to a group of women: "Do you girls masturbate at all?"
"Stop looking at me like that - I'll f***ing throw a bottle at your face, you goddamn whore."
DiCaprio and Maguire claim they thought they were appearing in a short film and did it only as a favour for a friend.
But when they discovered the final product was actually a feature film and the director was shopping it around to distributors, they tried to block its release.
The producer, David Stutman, took stars to court in 1998 and claimed that Maguire in particular was worried "some of the improvisational comments he had made during the film revealed personal experiences or tendencies that would undermine the public image he and his manager were trying to protect".
"Accordingly, they set out to do everything in their power to stop the film."
DiCaprio and Maguire successfully sought a ban for the film ever being screened in the US or Canada and that ban remains to this day.