These days, if a film is successful, it's almost guaranteed that they will be having a sequel and many screenwriters leave cliffhangers and loose ends that can be picked back up in a follow-up.
Some films, however, have the ending tie up all the loose threads, which means that when the studio demands another money-spinning film, they are forced to untie those threads and undo the efforts that they put into tightly wrapping up the first film's ending.
In films such as...
10. Pirates of the Caribbean: Dead Man's Chest
After Captain Jack Sparrow defeats Hector Barbossa and the immortal crew of the Black Pearl, he escapes execution for piracy and sails off into the distance on the Black Pearl with all of the treasures from the crew's decade-long plunder; Will and Elizabeth meanwhile, finish the film happy and in love, with her dad Governor Swann pardoning Will and giving him his blessing for them to marry.
Then, when the second film begins, on Will and Elizabeth's wedding day, the pair are arrested for allowing Jack Sparrow to escape and thrown in jail, completely ruining the happy ending that they'd earned in the first film.
Meanwhile, Jack Sparrow's wealthy life aboard the Black Pearl is instantly halted when Davy Jones demands that Sparrow join the crew on the Flying Dutchman to repay him on a deal they made 13 years ago.
So all-in-all, all of the characters' happy endings lasted the length it took for the second film to be released.
9. Austin Powers: The Spy Who Shagged Me
Having been unfrozen in the '90s, Austin Powers spends International Man of Mystery trying to adjust his free-spirited Swinging Sixties ways to the 1990s, ultimately finishing the film marrying Vanessa Kensington, the daughter of his '60s sidekick.
The Spy Who Shagged Me, which joins Austin and Vanessa on honeymoon, reveals that Vanessa is one of Dr. Evil's fembots, who then attempts to kill Austin before self-destructing.
After a moment of grieving, Austin then reverts back to his swinging, immature old ways.
Of course, the Austin Powers films were a parody of the James Bond movies that featured Bond ending the film with a beautiful girl, yet there would be no sign of her in the next instalment.
8. National Treasure: Book of Secrets
In the first National Treasure, Benjamin Franklin Gates and his friend Riley steal the Declaration of Independence, much to the horror of Dr. Abigail Chase, an archivist at the National Archive
Abigail is then thrown into the adventure, unwillingly at first, but then assists Ben and Riley solving clues and riddles to assist them to uncover the treasure, and at the end, Ben and Abigail have started a romantic relationship.
The second film begins and it's revealed that the pair have split up again because Ben always had to have the last word.
Ben and Riley are on a new adventure, and Abigail tags along (reluctantly at first), including coaxing her new love interest, Connor, a curator at the White House, into letting Ben into the Oval Office.
At the film's conclusion, without mention of her new boyfriend Connor, Abigail decides to take Ben back.
7. Bridget Jones's Baby
Having spent two films repeatedly breaking up and getting back together again, at the end of the second Bridget Jones's Diary, Mark Darcy finally proposes to Bridget and all is finally right with her love life.
Fast-forward to Bridget Jones's Baby twelve years later, and despite them having spent two films realising that they were supposed to be together, they have split up.
Mark has married someone else, but when meeting Bridget again, he tells her that he is getting divorced and Bridget and Mark inevitably end up in bed together, as not long after Bridget finds herself pregnant with two possible fathers - Mark or a man named Jack Qwant.
Just like Mark had done with Daniel Cleaver in the two previous films, he and Jack Qwant vie for Bridget's attention in hilarious and slapstick ways, before a DNA test reveals that Mark is indeed the baby's father.
The film then skips forward to one year later, and its Bridget and Mark's wedding day, as the pair have once again decided that they are meant to be together... for now.
The sole survivor of the deadly alien's attack on the crew of the Nostromo in the first film, in Aliens, Ripley is sent to assist a group of Colonial Marines to investigate a disturbance on the LV-426 moon - where the crew of the Nostromo discovered the Alien eggs.
After a fight with the Queen Alien with the iconic power loader, Ripley plots a route back to Earth and goes into hypersleep with Hicks, the badly damaged android Bishop and Newt, the young girl that Ripley looks after throughout the film.
The third Alien film then opens with Ripley not successfully touching down, rather landing in another hostile environment - a maximum security male-only prison on the barren world of Fiorina Fury 161.
Of course, she has the rest of the Aliens crew that entered hypersleep with her at the end of the film. Oh wait no, they've all died in a fire on the spaceship and Ripley is woken up once again as the sole survivor from the ship.
Oh, and an Alien managed to stowaway on the ship, survive the fire and land on the Fiorina Fury 161 to cause more mayhem.
5. Men in Black II
After Agent J and K destroy the alien bug which is trying to start an intergalactic war, the grizzled Agent K tells new recruit J that he was training as a replacement rather than a partner, and neuralises his memories returning to his normal life.
Laurel Weaver, a medical examiner who got mixed up in the alien battle, is recruited as J's partner, Agent L.
Agent L doesn't even feature in the sequel, with no explanation for her absence (in real life Linda Fiorentino didn't want to return to the role), and Agent J needs Agent K's memories to defeat a dangerous new enemy.
J helps to bring back K's memories, and the pair then continue as Men in Black partners, and the events at the end of the first film are completely disregarded.
4. The Hangover II
At the end of the Wolfpack's adventures in Las Vegas in the first Hangover, the trio have learned about themselves and have become better people then they were before.
When the second Hangover film rolls around, the group head to Thailand for Stu's wedding, and the character development from the first film is completely wiped clean.
Alan once again drugs the group, despite the events of the first film, and the trio then have to find out what happened to them the previous night and where they have left another one of the group who has disappeared.
3. RoboCop 2
After Officer Alex Murphy is killed by Old Detroit crime boss Clarence Boddicker, most of his body is replaced with cybernetics and he is 'resurrected' as RoboCop with a robotic voice and mannerisms.
At the end of the film, RoboCop has satisfied his quest for vengeance against Boddicker and kills corrupt OCP senior president Dick Jones, his voice returns to Murphy's speaking voice and has come to terms with the fact that he's the same man he always was.
In the less successful sequel, after RoboCop returns to speaking like a robot and he spends most of the film being conflicted about whether he is a former human being, or had the memories implanted despite resolving this at the first film's finale.
This goes as far as RoboCop telling his wife that the face under his headset is just a copy of Alex Murphy's original face.
2. Rocky II
When the failed boxer Rocky Balboa impresses the overconfident Apollo Creed in their Rocky fight with his refusal to be knocked out, Creed tells Rocky: "Ain't going to be no rematch!" before the final bell rings leaving both fighters exhausted.
Yet, Rocky II picks up the story immediately after Creed wins the fight in a controversial split decision, as both fighters are taken to the same hospital, and he instantly forgets his promise to Rocky about a rematch, claiming that Rocky's hard-fought effort was a fluke.
Creed then challenges Rocky to a rematch, but 'The Italian Stallion' states that he has retired.
Creed then goads Rocky into changing his mind and the pair then pick up their rivalry, completely reversing the ending of the first film.
1. Ghostbusters II
At the end of the first Ghostbusters film, the ghost-busting team of Peter Venkman, Ray Stantz, Egon Spengler and Winston Zeddemore are lauded as heroes by the people of New York after destroying the giant Stay Puft Marshmallow Man (that they created, incidentally) that was housing the spirit of the 'destructor' summoned by Gozer.
Despite saving New York City from demi-god Gozer, and having hundreds of people cheering them on, when the sequel begins, those people have changed their tunes, believing that the whole thing was a publicity stunt pulled by the Ghostbusters.
They are sued by the sceptical city authorities, who also bar them from investigating the supernatural, which destroys their reputation forcing them out of business; and Venkman's girlfriend Dana - who he spent most of the first film chasing - has married (and then divorced) someone else and had a son.
So when Vigo the Carpathian causes a supernatural scene, through a wacky sequence of events, the Ghostbusters are allowed to continue busting ghosts, and when they manage to destroy Vigo, thanks to assistance from the Statue of Liberty, the Ghostbusters are once again heralded as New York City's saviours and the mayor gives them a Key to the City.
Who knows how they'd have undone it again if there was a third film.