Some films seem like they're never going to get made (Ghostbusters 3 - we're looking at you), while some films have the intention to never be made.
Those films are mostly fake trailers to feature in other films for one reason or another, and here are 14 brilliant fake trailers from the likes of Tropic Thunder and Grindhouse that we wish would actually be made into feature films.
Teresa: The Making of a Saint
Can you imagine Megan Fox as a nun? Of course you can't.
But in How To Lose Friends And Alienate People, she's an upcoming Hollywood starlet who features as the legendary Mother Teresa in her early days.
Of course we're pretty certain that Mother Teresa's early life didn't contain so much illicit liasons.
Possibly the best of the fake trailers to accompany Quentin Tarantino and Robert Rodriguez's ill-fated Grindhouse project.
Don't is an homage to the British Hammer horror films that were made with production line efficiency in the 1960s and '70s.
Directed by Edgar Wright and featuring,among others, Rafe Spall, Simon Pegg, Nick Frost, Peter Serafinowicz plus a voice-over from Will Arnett, Don't looks like a gore-soaked silly horror that takes itself too seriously.
The Entourage biopic of Colombian drug load Pablo Escobar, with the lead played by Vincent Chase in a fat suit.
In the show, the screenplay was discovered on the New York City subway and received damning reviews at the Cannes Film Festival before going direct-to-DVD.
If this is the trailer of the (in-show) film, you can see why.
Eli Roth's contribution to the Grindhouse fake trailers, a holiday-themed slasher film in the style of Halloween, My Bloody Valentine and April Fool's Day.
Thanksgiving sees a killer pilgrim on the loose on Thanksgiving weekend, with lots of blood, gore and pretty disturbing slayings.
Scorcher VI: Global Meltdown
The world's highest-paid, highest-grossing action star Tugg Speedman kept replicating the success of the original Scorcher, only, just like real life, for it to become dull and repitive.
To buck the trend Scorcher VI sees the world on the brink of freezing with Speedman continuing to utter those cheesy acton flick quips.
Hamlet (with Arnold Schwarzenegger)
The Last Action Hero's 'film within a film' has Arnie's character Jack Slater appearing in Shakespear's Danish play Hamlet.
Unfortunately for the memory of the bard, Schwazengger doesn't deviate too much from his gun-toting, violent character and Hamlet becomes a lot more explosion-filled.
Movie: The Movie
From Jimmy Kimmel Live, Jimmy gathers his best A-list mates to feature in a trailer for what could be the best, or worst, film of all time.
All of the movie cliches and tropes are covered in this eight minute trailer and there's some unusal storylines in the incredibly silly Movie: The Movie.
With Tropic Thunder's Tugg Speedman suffering from a career stall (see Scorcher VI: Global Meltdown), he attemtped to go for an Oscar-bait role to show off his serious acting credentials.
Only, unlike I Am Sam, Forrest Gump and Rain Man, no-one warned Speedman: "Everybody knows you never go full retard."
Werewolf Women of the S.S.
Nicolas Cage stars as Fu Manchu in Rob Zombie's tribute to the Nazi exploitation films like Ilsa, She Wolf of the SS and Fräulein Devil.
According to Zombie: "Basically, I had two ideas. It was either going to be a Nazi movie or a women-in-prison film, and I went with the Nazis. I've always found that to be the most bizarre genre."
Seriously talented method actor Kirk Lazarus' Brokeback Mountain-esque Satan's Alley, winner of the Bejing Film Festival's Crying Monkey.
The Oscar bait sees the forbidden love between two gay monks (Lazarus and Tobey Maguire) in a 12th-century Irish monastery.
We get a glimpse of the Austin Powers biopic in the beginning of Goldmember, directed by Steven Speilberg and starring Hollywood A-listers Tom Cruise, Gwyneth Paltrow, Kevin Spacey and Danny DeVito.
It's a more straight-laced action flick than what we get in Austin Powers, which makes us wonder whether it'll be asgroovy as the actual International Man of Mystery.
Machete Kills Again in Space
Machete was a Grindhouse trailer that was made into an actual film, then had a sequel, Machete Kills.
But harking back to their roots at the end of Machete Kills, we're given a parody trailer seeing Danny Trejo blasting into space.
A play on films like Jason X, we'd still love to see the Mexican assassin going into space.
Jack Black's low-brow comedy in Tropic Thunder which sees Jeff Portnoy playing a fat, flatulent family in The Fatties: Fart 2.
An obvious finger point at Eddie Murphy playing the whole family in Nutty Professor II: The Klumps and being fond of passing wind.
Friends: The Movie
Our favourite sitcom finished over 10 years ago, and there are scores of people still missing the six main characters.
So it reopens those wounds when we see the group gathering again to feature in the pretend Friends: The Movie.
It happened to Sex and the City, one day...