They started it all in the ending of doctor strange: the idea of some fresh mystic to stir time into the celestial pot.
Then they used it to complicate the bad end of fighting thanos, then they used it again in the good end of defeating him.
There you have it: try the same countless times in hopes to bore the beholder.
Gues what: he got that fed up he started doing his own what ifs and we can all see where that led.
For whatever reason, the mentor of our MC left everything behind and started the biggest rival faction.
All of it was in good faith tho, as Our whole life got to flourish because of it, along with the queen and everyone dear.