Transcription
Did you ever realize that Tony Stark might have already known what would happen on Vormir?
When all the Avengers split up to collect the Infinity Stones, Natasha and Hawkeye were sent to get the soul stone. But as we know, only one of them came back. Natasha sacrificed her life so the Avengers could win.
When the team returned, everyone was heartbroken. Thor, Steve, Bruce, each one of them was grieving and blaming themselves. But Tony, he was strangely calm, almost like he had already accepted it.
Back in Infinity War, when Tony was fighting Thanos on Titan, Nebula mentioned that Thanos went to Vormier with Gamora, but came back alone with the soul stone in his hand. "He took her to Vormir." "He came back with the soul stone." Tony put the pieces together right then. He knew what it meant. Someone had to die to get that stone.
So when he sent Natasha and Clint to Vormir, deep down, Tony probably knew that one of them wouldn't return. That quiet acceptance we see in Endgame, that wasn't shock. It was grief he'd already prepared.