Board Thread:Questions and Answers/@comment-25322628-20180503033850/@comment-4851903-20180506130341

Yeah and is no surprise how he made the right move by saving Stark because he also ended up being in the lucky half that wasn't erased. Strange was against giving the Time Stone for the majority of the movie until he saw all those futures, that's where he probably realized the only way to win was to surrender the very thing he swore to protect, hence why the line "it was the only way" before vanishing.