Why And When Did Thanos Nearly Give Up His Destiny Before?
Thanos drops a very interesting detail into his final conversation with Gamora on Vormir. Though it’s revealed that he loves her dearly, the Mad Titan ultimately sacrifices his daughter in order to claim the Soul Stone. His reasoning is that he once almost turned away from his destiny in the past, but he won’t make that mistake again on this occasion.
This sounds like Thanos once had the opportunity to unite the six Infinity Stones, or perhaps just claim the Soul Stone, before now but decided not to at that point. Presumably, for the same reason that he almost didn’t this time – to save the life of someone he loved. Perhaps Thanos had a family on Titan and didn’t enact his plan to halve the population in order to save them… But they ultimately died when the planet destroyed itself.
This is just speculation on our part, though. The MCU’s version of Thanos contrasts with the comics’ portrayal to such an extent that we can’t look to the source material for answers, either. It’s likely that this tease will be further explored in Avengers 4, though.