By now, audiences are primed to expect the ending of a movie not to really be the end. Even away from the dead cert stinger movies in the comic book movie genre, the gripping fear of missing out on any hidden content makes hardy souls endure what feels like hours of scrolling names, occasionally for no pay-off at all. That's why so many people can now be seen furiously Googling "does this movie have a post-credits" well before the Best Boy gets a name-check.
Obviously, most movies still don't have stingers, but with shared universes and sequelitis continuing to grip Hollywood, you can usually rely on blockbusters of a certain size to have something hidden. And more often than not, they'll promise something for the future - like a built-in hype generator to keep fans talking about the brand. Unless they're made by James Gunn and then they're just for fun, mostly.
But sometimes, even with stingers that seem to be leading somewhere, reality gets in the way and for whatever reason - it's usually money, let's be honest - the possibilities teased in the post-credits don't ever come to fruition. They end up being frustrating dead-ends, in other words, and it's happened a fair few times...
If you were hardy enough to sit through the credits of Justice League, your reward was seeing Lex Luther broken out of prison and celebrating Superman's return with Deathstroke on his yacht, while proposing they team up to take down on the Justice League. A very nice tease, but sadly, it probably won't amount to anything after the film was a relative bomb.
It hasn't fully been confirmed as a dead-end just yet, but there are some serious questions over another Justice League movie at the minute, so the great idea of a league of villains to face the Justice League might end up going nowhere.