Thread:Elledy92/@comment-26838855-20190425183005/@comment-26838855-20190429143349

This is something that I do think the film didn't quite explain well enough, giving it more of a hand-wave. But there's two possible explanations:

In moving a stone at all from the path it previously followed, you have set the new timeline in motion, so it's not that it only splits once you've plucked it from the timeline fully. This is the explanation I think is the case, judging by the Ancient One scene.

Or, less likely:

If you don't think of time as unfurling in order and just look at it as an already existing line (with splinters), then the timeline splintered in all the Time Heist spots because of the removal of the stones, but that the splinter began when they arrived in those spots because essentially the timeline is already established, fourth-dimensionally speaking, that it will splinter in the Time Heist incidents but not splinter for Steve and Clint because there's no messing with the timeline. If you think about time the other way around (which, fourth-dimensionally speaking, is fair), you would hit the splits from the Stones being removed, which would be adjacent to the main timeline, and then the line you would draw after that would converge into the main timeline because you're going backwards. And in that diagonal line, that's when the Heist occurred. It's a tricky and complicated excuse, but if you just think of time as laid out, which it is as it's just the fourth dimension that we are experiencing as a series of three-dimensional moments, then the "timeline knows", if you will, that it will splinter in those Time Heists but won't for Steve and Clint.