Warning: This article contains spoilers for several Marvel Cinematic Universe movies and TV series. Proceed with caution.
The Marvel Cinematic Universe is a bit stale if you don't know what to do with Marvel's Agents of S.H.I.E.L.D., the popular ABC television show about Agent Phil Coulson and his A team. After the first Avengers movie, many fans were left confused about how the series integrates into the Marvel Cinematic Universe.
Phil Coulson, played by Clark Gregg, became the most trusted agent for Nick Fury (Samuel L. Jackson) throughout Phase 1 of the Avengers, and viewers later learned that he loved the First Avenger (Chris Evans) so much that he was involved in the design of Steve's updated Captain America uniform.
When Scarlett Johannson tells Steve that he has vintage Captain America trading cards that he wants him to sign, Coulson is stabbed in the back (literally) by Loki (Tom Hiddleston).
When it was announced that Gregg would reprise his role as Coulson in his own television program, fans were left confused. While Coulson was mentioned numerous times as a fallen hero, no one mentioned that he somehow miraculously survived.
Coulson did not survive Loki's assault, but was revived through an experimental program called Project T.A.H.I.T.I. This proves that Agents of S.H.I.E.L.D. are not part of the usual Marvel Cinematic Universe. If Nick Fury had not tested Project T.A.H.I.T.I. on Tony, it would be a reasonable assumption that it would not have existed.
Agent Mobius (Owen Wilson) points out Coulson's death as one of the reasons Loki is such a bad person in the Disney Plus series. While Loki solidifies the fact that Agents of S.H.I.E.L.D. cannot be in the main universe, it also opened the way for it to happen in the future.
The possibility of an alternate timeline where Project T.A.H.I.T.I. brought Agent Coulson back to life is now a reality. One minor tweak to the timeline and Coulson's death, rebirth, and happily ever after may be officially canonized.