Joss Whedon admitted that one of the reasons he decided to walk away from the Marvel Cinematic Universe was the amount of concessions to the studio he was forced to make during Avengers: Age of Ultron, which would go some way to explaining why the second big screen outing for Earth’s Mightiest Heroes is generally regarded as their weakest adventure.
One of the most heavily-criticized aspects of the story is when Thor simply ups and disappears when the gang are hiding out at Hawkeye’s safehouse, before the God of Thunder goes to track down Erik Selvig so that Chris Hemsworth can climb into a pool for his contractually-obligated shirtless scene that didn’t factor into the rest of the movie at all.
Of course, Thor’s brief sojourn was explained in more detail thanks to a deleted scene that was available on the home video release, but there was little explanation or context given to the sequence in the version of the movie that hit theaters. However, based on the ending of Infinity War, the Odinson’s earlier prophecy after being manipulated by Wanda Maximoff ended up making a lot more sense.
During his vision, Heimdall calls Thor a destroyer that will lead the Asgardians to hell, which at the time seemed like the kind of throwaway scene that future installments in the MCU might never actually get around to paying off. However, during Infinity War’s final moments, Thor fails to prevent Thanos from wiping out half of all life in the universe because he didn’t go for the head, which inadvertently made him a destroyer as a result.
Not only does this set up the character’s entire arc for Endgame where he felt personally responsible for the Snap, but it also intentionally or not pays off what looked to be an abandoned plot thread from Avengers: Age of Ultron, with Thor’s failure to decapitate the Mad Titan despite possessing a weapon powerful enough to kill him the last thing that happens before Thanos snaps his fingers.
Whether the filmmakers intended it or not, it goes down as yet another example of how it can often take years for seemingly-innocuous scenes in the MCU to paid off in any sort of meaningful fashion, even if it was always supposed to be part of the plan.