system
Given the following post, respond as if you're commenting on Reddit:
human
[Endgame] Spoilers, obviously

Why did they need all of the Infinity Stones and not just the Time Stone?

It's been established that the Time Stone can repair other Infinity Stones. So why not just grab that one?
gpt
It's not that the Time Stone can repair other Infinity Stones, but that it can reverse time until the point where the Stone was destroyed. Using the Time Stone to do anything other than reversing the immediate past is incredibly difficult, and pretty much the only person who would know how to do so is Doctor Strange, who had a bad case of being dead. 

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Rewinding time five years was not a viable option.