Previously - or, perhaps, much, much later:
"Yeah, we got one advantage," says Stark, "he's coming to us. We'll use it."
"All right, I have a plan." He turns to the others. "Or at least the beginnings of one. It's pretty simple. We draw him in, pin him down, get what we need. Definitely don't want to dance with this guy, we just want the gauntlet." And - "Are you yawning?" he snaps at Drax. "In the middle of this, while I'm breaking it down? Huh? Did you hear what I said?"
"I stopped listening after you said that we need a plan," replies Drax.
"Okay, Mr. Clean is on his own page," Stark says.
"See, not winging it isn't really what they... do," Quill replies.
"Uh... what exactly is it that they do?" asks Parker.
"Kick names," replies Mantis, confidently. "Take ass."
"That's right," affirms Drax.
Stark stares for a moment.
And starts to realize that this really might be the end.
Dr. Stephen Strange, Sorcerer Supreme, defender of the cosmos, isn't paying much attention to any of this debate. His eyes aren't open, but he's rapidly looking back and forth anyway, because he's seeing through the view of the Time Stone.
The Time Stone can't actually see exactly what will happen in the future, but it can view each of the limitless possibilities that might come from this, and that's what Strange needs, if he wants to formulate a plan that will defeat Thanos.
The problem is... none of them seem to involve defeating Thanos.
He has looked through millions, literally millions of futures, and in each and every one of them, Thanos wins. In the vast majority, he simply crushes them all in battle, regardless of what plans they come up with. In a few, they at least get closer - maybe by briefly wounding him, or grabbing his Infinity Gauntlet, in a few rare ones - but even in those, he manages to get it back within a few moments. Strange eventually found a few hundred timelines in which Thanos was defeated on Earth by blowing up the planet and killing everyone there, and he is seriously considering doing that because there is nothing better. Except that even in most of those, someone else eventually finds the scattered stones and causes more chaos, and if all of the superheroes are dead, they can't stop them.
A little after twelve million, he starts looking for timelines in which Thanos wins at first, but the surviving Avengers reunite and manage to defeat him later. But the problem with those is that not only are they vastly outnumbered, but Thanos usually destroys the Infinity Stones after a week or so, meaning that even if they do manage to defeat him, they won't have anything they can use to bring back all of the people Thanos will inevitably kill.
But he's still looking, and looking, and -
He's crossed fourteen million.
Fourteen million timelines, and not a single one has presented him with anything that doesn't involve the murders of at best many billions of people.
Why didn't he do this before now? He had heard of Thanos! He was on the list of possible threats to the universe - not anywhere near the top of the list, which in retrospect was a big mistake, but still, he should have tried to find out what would have threatened Earth, and fix it then. But now it's too late, and he can't change -
He could change things...
The Time Stone can't rewrite history on a scale of more than a few minutes, not on its own. But maybe in conjunction with other Infinity Stones... hmm. The Mind Stone's still on Earth. Maybe he could use it, and the Time Stone, to send his mind back into that of his younger self?
He looks through a few more timelines. Nope, looks like that doesn't work. First, because it would be tricky to do with his own mind instead of someone else's, and second, because - oh.
He needs the Soul Stone, too.
The problem is, Thanos already has the Soul Stone.
Okay. Are there any timelines in which they can steal the Soul Stone from Thanos, and then get both it and the Time Stone back to Earth, and get the Mind Stone out of Vision in time to send somebody back in time?
Well, he'll keep looking.