Just a heads-up, the concept of this largely depends on having watched the fifth season of Marvel's Agents of S.H.I.E.L.D. as well as Avengers: Infinity War. So... spoilers for that follow.
Okay, to start things off: In the movie, Dr. Strange sees fourteen million, six-hundred and five possible futures and only saw one victory for the heroes, which happens to involve Thanos winning anyway. The question is, in the span of a few hours (or weeks, as we now know will be between that moment and Endgame, which only Dr. Strange would be aware of), how could so many timelines diverge? Presuming that the premonitions he counted did not include divergent timelines created by innocuous events across the universe and only focused on events that would take place on Earth and Titan, I propose to answer that question using Agents of S.H.I.E.L.D.
In the fifth season of Agents of S.H.I.E.L.D., in which most of the events detail the cast's adventures leading up to Infinity War, Team Coulson finds themselves in a future where Earth was destroyed not by Thanos, but by the so-called "Destroyer of Worlds", eventually revealed to be Graviton/Glenn Talbot, drunk on the power of Gravitonium and wanting to absorb more power while Thanos is causing trouble elsewhere. It is shown that they seem to be stuck in a time loop, where Team Coulson gets pulled into the future, finds out about the apocalypse, goes back, tries to stop it, and fails, leading to the survivors of Earth ending up on the Lighthouse in space, and a future(?) version of Yo-Yo reveals that nothing they did had any effect on stopping the destruction of Earth. However, it was explained in the middle of the season by creators that the first timeline we saw, shown as Robin Hinton's flashbacks, were from the original timeline where Team Coulson did not go into the future, meaning that what was happening in the first half of the season was the latest in a series of ever-so-slightly-different loops trying to set right what went wrong.
Anyway, what if those loops constituted a sizeable number of the outcomes that Strange saw?
Five down, one to go.
Thanos vanished from his former home planet, using the Space Stone to transport himself to the planet Terra, which the residents knew of as Earth, in an instant. He appeared on a grassy plain, which he noted was littered with the corpses of his Outrider attack dogs and native warriors. He took note of the planet's remaining defenders. Two of them he knew to be members of the Guardians of the Galaxy, the only two whom he had not yet confronted. There were no sign of either Cull Obsidian or Proxima Midnight. He saw Corvus Glaive's dead body and determined that his other loyal children had not survived the battle.
Not too far from Glaive's corpse, he took sight of the red-bodied android whose forehead housed the Mind Stone that he desired. Not wanting to waste any more time, having had his fill of fighting the heroes on Titan, Thanos made his way over to his prize.
However, the defenders refused to make the fight easy for him. A man donning an armor similar to Stark fired upon him. Thanos used the Space Stone to telekinetically throw him aside. A man with a metal arm fired his gun at him, but Thanos blasted him away with a pulse from the Power Stone. A bald woman threw a spear, but Thanos stopped it in midair with the Space Stone and used the Power Stone to blast her away and raised stones from the earth to trap her companion. A sapient tree attempted to snare Thanos with roots and vines, but he broke free effortlessly.
While he fought, he saw a young woman hold a short conversation with the crimson android. She then began to fire an energy beam at the Mind Stone in his head. She aimed to destroy the Infinity Stone before he could get to it. And he could tell that she had a very good chance of succeeding. He could also tell that she was acting with reluctance, as she knew that destroying the Stone would destroy the android, and she had no desire to do that.
And Thanos had no desire to watch her destroy the stone.
He charged forward, but a bearded man stepped in his path. He punched the giant with arms mounted with metal shields. Thanos put his arm forward to push him aside, but the man stood his ground, grabbing the larger hand and holding him back with all his strength. Thanos was amazed by the man's strength of will and strength of arm. He was actually holding him back!
But Thanos saw the young woman continue to assault the Stone with her power, and he decided to cease his dallying. He punched the man with his free hand to knock him down.
He took a step toward his quarry, but nearly stumbled when he felt a fierce tremor beneath his feet. He saw all others quiver in their efforts to regain their footing and even witnessed the young woman falter, so he knew that it was not just him. He was not sure what had happened, but he decided to ignore it and make his way to the Stone before the young woman resumed her attack on it.
The young woman regained her focus and, after a brief hesitation, fired her energy beam at the Mind Stone again. Thanos charged toward her. She saw the purple warlord coming and turned one hand away from the android to fire a beam of energy at him. However, using the Power Stone to boost a shield, Thanos guarded against the attack with his Gauntlet. However, he was forced to slow down his march as he pushed against the constant beam. He realized that the woman's powers had been derived from the Mind Stone by some means, thereby giving her the strength to attack the Stone at its molecular core.
Another tremor, this one greater than before, struck. Both Thanos and the young woman fell to the ground. The woman's first beam fell away from its mark before dying down, carving a line into the android's face and chest. Several trees fell. Thanos watched a rift break in the ground in front of him. What was going on? What calamity was striking this planet?
Still determined to do her duty, the young woman turned to face the android and fired her beam once again. Thanos crawled forward, climbing across the growing rift.
The Stone would have exploded right then. But something impeded the young woman's efforts once again. There was yet another tremor, the force of which caused everyone to collapse completely. The earth exploded beneath them. A nearby building sank into the ground. Purple rocks spiked and burst out of the ground.
Thanos had diverted his attention away from his goal and focused on trying to figure out what was happening. He saw a bizarre substance float from the cracks in the earth. It appeared to be a liquid metal, like silver in color while also reflective like chrome. He saw the substance loop over some of the fallen warriors, and they started to float in the air.
Could it be?
Gravitonium?
There was another quake. Purple rocks exploded out of the ground, blowing the earth around it to bits. A stone hit Thanos in the chest, blasting him a hundred feet back with raw kinetic energy. He fell into a widening crevasse, unable to wrap his mind around the events that had occurred.
After about a minute of falling, he felt his descent slow until he came to a stop. Looking around, he saw a massive cavern filled with the purple rocks. But that was not all he saw. The silvery metal floated around him, keeping him afloat with its anomalous gravity-manipulating properties. He suddenly wished he was still falling, as his current position gave him a clear view of what was happening to the planet.
The earth around him cracked and crumbled. Chunks of rock broke off and started to float away. The purple rock exploded from the inexplicable force that was tearing it apart.
In what he knew would be the planet's last moments, Thanos noticed the Gravitonium inch closer and leech toward his arm. He tried to use the Infinity Gauntlet's powers to drive it away, but as it wrapped around his wrist he realized that he could not feel his fingers.
Thanos sighed, as he knew that he would not be saving the universe. His efforts to carry out a mission that would affect all life on every planet had met their end due to something he could never have expected: a disaster that would bring an end to only one planet.
He closed his eyes, not wishing to bear witness to the cataclysm as it reached its climax.
He was barely conscious when he felt the earth-shattering KABOOM