To go along with my earlier theories about Avengers 4: Relating to the different scenarios that Dr. Strange saw playing out, and his "this was the only way" comment, I was thinking that the outcome of Infinity War was pretty much set to play out about how it did in every single scenario. "Winning" is not somehow about altering that stage of the timeline--defeat and the nature of that defeat were inevitable. But perhaps Strange was merely manipulating who would and would not survive the snap. If you think about the idea of looking at different potential outcomes, and there is only one where they "win," you can basically boil it down to statistical analysis. And perhaps that statistical analysis does not depend on the facts of what actually happens in the battles, but on certain combinations of key individuals surviving and not surviving the snap. In other words, "winning" at some point down the road is determined by something along the lines of "individuals A, B, C, D... must survive the snap; individuals P, Q, R, S... must not." And maybe for a lot of you, this is a "well, duh!" theory. I mean, it is heavily implied in Infinity War that Stark's survival was key. But it had not occurred to me until just now that there may have been a necessary bigger combination of individual survivors and nonsurvivors that had to be set up for the "winning" scenario.
EDIT: I mean, if you think about it, Strange knew there was only one "winning" outcome. And he apparently knew that he would have to give up the time stone to accomplish that. So why engage in that big fight on Titan? He has to have been manipulating the outcome somehow. I guess one possible explanation is that he was buying time because he needed certain events to happen elsewhere. But another explanation is that he was manipulating who would and would not survive. I think Thanos has some (or possibly complete) control over who remained and who did not. I think, left to his own devices, Thanos leave the original Avengers intact unless he has to kill any of them off to get one of the stones to begin with. Sure, they are dangerous. But he also respects them. And I think he basically sees them as "fit enough to survive." On the flip side, I think he plans on killing off Starlord, Drax, and Mantis for being associated with Gamorra and trying to stop him on Knowhere (I don't think he particularly cares about Groot and Rocket, if he even specifically knows of them). I think Strange knows that the original Avengers must live, and that all the heroes on Titan other than Stark and Nebula must not survive (Strange in particular). Maybe Strange sees that he will have to communicate back from "the other side." Dunno. But in any case, maybe he fights so hard and uses so much of his own bag of tricks to make sure that Thanos takes them all out with the snap. Other than Stark, and Strange manipulates the fight to stop it and secure Thanos' promise to spare Stark at the last possible moment. And he knows Thanos will spare Nebula because she is still his daughter, and despite Garmorra being the favorite and torturing Nebula, he still "loves" her in some twisted way. But everyone else MUST go. There could certainly be other key people who either had to survive or had to not survive, but I think the original Avengers and Nebula surviving, and the remaining heroes on Titan not surviving were somehow key, and that Strange manipulated that specific combination (and possibly others) with his actions.
Anyhow, some more fun (or not) morning ramblings...