The post-credits scene of Avengers: Infinity War saw Nick Fury send out a cosmic Mayday for Captain Marvel's help - but why had he never used it before? Viewers have only been to speculate, but the official Captain Marvel Prelude tie-in comic offers a few major clues.

Nick Fury first met Captain Marvel in 1995 during the events of her solo movie, when he's just a junior S.H.I.E.L.D. operative. When their adventure is over, Carol will presumably head off into space (or, perhaps, into the Quantum Realm), and will leave Fury with a modified pager to summon her if he ever needs her help. But why did Fury wait so long before using the pager? He didn't choose to send for Captain Marvel's help during the Chitauri invasion in The Avengers, for example, nor when Ultron was attempting to initiate an extinction level event and wipe out the entire human race in Avengers: Age of Ultron.

Related: MCU Theory: How The Quantum Realm Fits Into Captain Marvel

The official Captain Marvel Prelude comic offers the first clues. There's one brief conversation, set at the same time as the end of Captain America: Civil War, in which Nick Fury and Maria Hill discuss heroes. Hill is evidently disappointed in the Avengers, and doubting the wisdom of this entire initiative. "I've heard something else said about heroes," she observes caustically. "Never to meet them. They'll only ever let you down." It's an observation Fury objects to, and he gives a swift response; "Not all of them."

cobie smulders as maria hill in agents of shield

Eternally observant, Hill realizes that this seems to imply there's still another hero in play. "You got one we haven't called yet," she asks, clearly curious. "Might be helpful to have a backup plan in case the worst should ever come." In case readers were doubting this conversation was about Captain Marvel, Fury ends it with a simple response; "Nah. If we do our job right, we'll never be in a position of having to call her."

It's just a single brief conversation, but it shines a light upon the relationship between Nick Fury and Captain Marvel. It seems Fury believes Carol Danvers is truly a hero who will never let you down, but also one he doesn't want to ever need to summon. He views Captain Marvel as the ultimate backup, a "Hail Mary" in the event everything else has fallen apart. Presumably the reason he didn't call Carol in during the Chitauri invasion, or during the Battle of Sokovia, was because he still had faith the Avengers would sort things out. By the events of Avengers: Infinity War, though, he's no longer confident the Avengers can do the job. They're divided, scattered to the winds, and Tony Stark is missing. When people begin to crumble to dust around him, Fury knows he's reached the worst-case scenario - and now he needs to call in somebody he can trust.

It's interesting that Fury will end Captain Marvel with such a high opinion of Carol Danvers. That dialogue suggests she'll succeed in earning his trust, and coming from a man who considers trust rather the Vibranium, that's pretty impressive.

More: Captain Marvel Theory: How Nick Fury Loses His Eye

The official Captain Marvel Prelude is available now from ComiXology.

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