It's been months since the release of Avengers: Endgame and fans are still devastated about Iron Man's death. Unfortunately, even the most powerful heroes couldn't survive a fight, and a new speculation might have hinted that Iron Man's death in Endgame was actually inevitable.
Redditor WolverineKuzuri93 posted a photo of a scene in Iron Man 1 that might be connected to Tony Stark's sacrifice in Endgame. The theory suggests Iron Man's arc reactor could have been the reason he wielded the stones without being incapacitated.
The photo shows screenshots from Iron Man where Tony and Yinsen were making the arc reactor as well as the first Iron Man suit. Yinsen tells Tony that the arc reactor could run Tony's heart "for 50 lifetimes." Tony replies, "Yeah. Or something big for 15 minutes."
This led the Redditor to believe that the reason why Tony held off the Infinity Stones and managed to take the snap was because of his arc reactor. If you recall, Hulk was able to reverse Thanos' snap to which it resulted in his arm being damaged. Some fans were convinced as well because the said theory explain why Tony was able to hold the stones off.
Although Tony pertained to his suit when he talked about "something big for 15 minutes," it couldn't be a foreshadowing for what happened in Endgame. Tony Stark was actually able to do the snap because the nanotech used in the gauntlet were the same ones used in his suit, the stones' energy were likely passed onto his suit which could have protected him while he did the snap. However, he still didn't survive it because the suit wasn't built to outlast the mission.
After all, out of the Avengers, he was literally the only one with the resources that were built to survive the snap, in which Doctor Strange has foreseen prior to facing Thanos one last time.
It is possible that the arc reactor could have played a big part in keeping him alive despite the snap, but it looks like that isn't actually the reason why Tony Stark was able to succeed the mission.
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