Sequels are the lifeblood that keeps Hollywood turning on its axis - pretty much any moderately profitable movie will have producers and studio executives scrambling to consider the commercial viability of another go-around or two.
And so it makes sense that filmmakers tend to include sequel-baiting setups in their movies, regardless of whether a follow-up has already been greenlit or not. After all, why not tantalise the audience with the promise of more to come?
Yet not all films are quite so craven and calculated with the manner in which they set up sequels, and sometimes it's basically entirely by accident, believe it or not.
These 10 movies all teed up sequels which eventually came to fruition, and though on the face of it the sequel-teasing seems totally deliberate and intentional, that actually wasn't the case at all.
From the writers and directors themselves, we've got stone cold confessions that these neon signposted sequel teases weren't originally supposed to do anything beyond entertain and enthrall the audience in a singular, closed-off way.
But studio heads didn't quite see it that way, with these potentially one-off stories becoming bonafide franchises in their own right...
10. Back To The Future
Back to the Future's iconic ending feels like such pitch perfect sequel-bait that it's difficult to believe that director Robert Zemeckis and co-writer Bob Gale didn't intend a franchise from the jump.
The film of course ends with Marty (Michael J. Fox) returning to his salvaged 1985 timeline and reuniting with Jennifer (Claudia Wells), before Doc (Christopher Lloyd) reappears in the DeLorean and insists the pair come with him to help save their future children. Oh, and the DeLorean can fly now.
Yet according to Zemeckis himself, this ending was never intended to be anything more than a silly, throwaway gag:
"We'd never designed the first Back To The Future to have a sequel. The flying car at the end was a joke, a great payoff. We thought this would be really hard to unravel and do again. But when you make a movie that's as successful as Back To The Future, it becomes this piece of corporate real estate. It becomes bigger than you as a filmmaker. You're basically given a decision: we're making a sequel, do you want to be involved in it or not?"
Given that Back to the Future grossed almost $400 million worldwide - more than 20-fold its budget - it's little surprise that Universal took that ending far more seriously than Zemeckis or Gale ever intended, and so a franchise - consisting of two sequels, shot back-to-back - was spawned.
Thankfully, despite Zemeckis' lack of initial interest in making any sequels, they both turned out pretty damn well with his involvement.