Marvel has been very stingy about plot details for Avengers 4, which has led some fans to go wild with theories concerning what happens in the movie. One theory purports Nick Fury having known a whole lot more than he let on, and that he actually knew about Thanos and The Snap years before the Infinity Stone hunt. Now, one Reddit theorist has taken it a whole lot further by saying that everything in the MCU has been preordained as part of Doctor Strange's end game.
A Reddit user by the name of sfmarch07 posted a very long and detailed theory about Nick Fury and Iron Man's role in Avengers 4. Built out of pieces from a few other theories, this new bit of fan speculation takes a deep dive into Nick Fury's role in the overall MCU, claiming that Jackson's character will get a vision of the future in Captain Marvel, in which he will see Thanos defeating the Avengers and wiping out half of the universe.
Per the speculation, Fury will be shown vital events, characters, and all the things that need to happen to make sure the Avengers actually defeat Thanos in the one successful outcome that Doctor Strange envisioned in Avengers: Infinity War. It's possible that Doctor Strange is the one showing Fury this vision in the first place.
This theory is essentially an explanation of how and why things have happened in the MCU the way they did. It attempts to explain why Fury did things like recruit Tony Stark first and gave him his father's box of secrets in Iron Man 2, as well as why he waited until the last minute to call in Captain Marvel. Theoretically, it was all part of a grand design to eventually defeat Thanos.
The other major part of this grand scale theory is that Tony Stark will have to make a big sacrifice in Avengers 4. It's been widely speculated that Avengers 4 will utilize time travel as the Avengers try to collect the Infinity Stones from the past. That means they will have to take the Soul Stone, which requires sacrifice.
Rather than Pepper Potts or Captain America making said sacrifice, the theory sets up Tony doing something else entirely: killing his parents. The guesswork states that Tony will travel back in time to infiltrate Hydra and order the hit on his parents. This would be the "hardest decision that any character has had to make in the entire MCU," as the theory puts it, adding that it would add an extra burden for the embattled Iron Man.
Fan theories can be really fun to read, and it's awesome to see the wild and different things that people think up. Personally, I don't think anything from this particular theory will happen -- especially the Tony-kills-his-parents part. That's straight-up nuts. The Nick Fury idea is interesting, but it robs all these movies of their stakes a bit if the Avengers was always strategically set up to win each battle in the end.
Will Nick Fury be revealed to be a huge puppetmaster? We'll have to wait and see in Avengers 4, which arrives in theaters on May 3, 2019.