The below theory — which I am about to break for you — is the most interesting, & well-conceived theory of Avengers speculation that I have ever come across on Reddit.

Excited? BE READY!!! 

THEORY CREDIT GOES TO…

This theory comes from Reddit user LoL-Guru, who put so much care into addressing every small detail of Avengers: Infinity War,

Anyway, LET ME EXPLAIN ALL THIS TO YOU:

Remember on Titan, when Thanos addresses Doctor Strange and says, "You never once used your greatest weapon"? He was, of course, referring to the Time Stone, and how Strange didn't use its power to help defeat Thanos right then and there.

Seriously, why didn't Strange use that bad boy and take another shot at the "remove the glove" plan? 

"An answer became clear when I remembered certain key details from the Doctor Strange movie," writes LoL-Guru.

"Even with the power to slow, pause, or reverse time, we have seen foes with the ability to ignore the Time Stone's effects," explains the user. For example, Kaecilius and his minions. 

"I think the Power Stone would have allowed Thanos to do the same; to bypass the power of the Time Stone," says LoL-Guru. This may also be why Thanos obtained the Power Stone first.

After seeing various futures, Strange understood this, and decided to formulate a different plan.

"When Dr. Strange pulls the Time Stone seemingly out of nowhere (like Loki did with the Tesseract) and floats it over to Thanos to save Tony, we can see two unique elements to this transaction," writes our theorist. 

Those elements are:

1. The Stone is glowing. Normally, Infinity Stones only glow when their power is being used.

2. Thanos doesn't physically grasp the Stone. Instead, he handles it by its green aura.

Now, let's pause and reflect on the unique behaviors — not powers — of each stone. This is important, I promise. 

Soul Stone: Can only be acquired in exchange for a soul.

Space Stone: Houses itself within a 4-dimensional cube in a 3-dimensional plane of existence.

Mind Stone: Has its own consciousness and can create consciousness (i.e. Vision).

Reality Stone: Can take on solid or liquid form, presumably gas as well.

Power Stone: So powerful it can destroy someone who even touches it.

So, then, what's the Time Stone's unique behavior?

"I would postulate that the Time Stone can be sent through time all by itself, going forward or backward," says LoL-Guru.

"How would you play keep-away with the Time Stone? Easy. Send it forward in time to where Thanos can't get it!" explains the user. "The problem is (as comic fans already know) Thanos is immortal, so he can wait it out."

Here's the kicker: "The Stone is glowing brilliantly because it's actually traveling back in time from the future!"

Rather than simply hiding the Time Stone in the future, Strange sent it there to be used by the leftover Avengers from Thanos' snap. Only after those Avengers have finished using it would it return to the present time.

Now, if this seems a tad confusing, stick with me, it'll all make sense soon.

We're assuming the Stone can travel through time, not space, which means it should appear on Titan after Thanos snaps (hold on, lemme get to why that is). 

And who's left to discover it but the lonesome Tony Stark?

"This is also why Tony needs to survive," explains the theorist.

"If the snap is inevitable, then he is the only one smart enough to A) Figure out what is going on when the Time Stone presents itself on Titan and B) Study the Stone in order to unlock the Quantum Realm (the same way the Mind Stone in the scepter allowed him to create Ultron)," says LoL-Guru.

Keeping everything in mind, this is why Thanos' gauntlet breaks after his infamous snap.

Thanos is "using a Time Stone from a reality where the Avengers have already won and sent it back in time," claims the user.

"The paradox of using a stone from a mutually exclusive reality breaks the gauntlet and helps advance Dr. Strange's plan even further because it cripples Thanos' ability to fight back when the Avengers start mounting their counteroffensive."

Plus, LoL-Guru thinks that certain clips from the Infinity War trailer corroborate this theory.

For example, remember the clip where Tony Stark removes his glasses while Wong and Dr. Strange stand behind him? That doesn't appear in Infinity War, but it could be a scene in Avengers 4 where Stark is retracing his steps.

and I'm  pretty sure you recall that the Hulk is shown in the trailer fighting in Wakanda?

According to theorist, that scene "may be from Avengers 4 when they have already gone back in time and must now face off against Thanos and his army again at Wakanda."

In other words, that could be an actual scene, it just hasn't happened yet.

To sum it up, from theorist point of view Doctor Strange did use his "greatest weapon," just not in the way Thanos imagined he would.

I don't know about you, but I'm betting on this whole time thing to save the day in Avengers 4.