LogFAQs > #900442446

The explanation given by Strange is reasonable enough. He saw all the possible outcomes and chose the one he did for a reason.

Attempting to use the full power of time stone against Thanos would not have guaranteed a victory. We've seen villains thwart the time stone before; Kaecilius was immune and he wasn't holding 4 infinity stones at the time. On top of that, Thanos shatters Strange's mirror dimension without even flinching. Strange's magic isn't unbeatable, like some people seem to think. Neither is the time stone. We've been shown this, more than once.

Destroying the time stone doesn't guarantee a victory either. Thanos has already leveled several civilizations. He balanced Gamora's planet without any infinity stones in his possession. He almost does the same to Earth in Avengers 1, without directly wielding the stones himself. He wipes out most of Asgardian survivors using the power stone. By the time Thanos arrives on Titan, he's probably already strong enough to conquer Earth. At this point, the only reason for him to complete the gauntlet is to take care of the rest of the universe in one fell swoop. Destroying the time stone doesn't save Earth.
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BKSheikah owned me so thoroughly in the 2017 guru contest, I'd swear he used the Lens of Truth to pick his bracket. (thengamer.com/guru)