The latest attempt at solving the mysteries of Avengers: Infinity War, like many others, deals with Doctor Strange's attempt to examine alternate futures, finding the one outcome where Earth's Mightiest Heroes actually defeat Thanos.
Of course, the movie doesn't turn out as expected when Strange gives up the Time Stone, allowing Thanos to succeed in assembling the Infinity Gauntlet and wiping out half of existence. As he tells Tony Stark moments before fading into nothing, "It was the only way."
The fan theory on Reddit states that Thanos and his sacrifice for the Soul Stone is key to the heroes' victory in Avengers 4, due to that particular Stone's place in relation to the others. With it, the Mad Titan is almost unstoppable with a huge power over life and death. Check it out below:
Why there was only one possible victory in Infinity War, and a rough time line of Avengers 4. from r/FanTheories
All in all, it's a convincing theory, but until we know a little bit more about Avengers 4, we're going to withhold placing bets on any of this actually taking place. Avengers: Infinity War was a huge surprise for Marvel fans, and it's likely that directors Joe and Anthony Russo have something surprising in store for the final part in this epic crossover.
We'll see how Earth's Mightiest Heroes prevail against Thanos when Avengers 4 premieres in theaters on May 3, 2019.