In Avengers: Endgame, speaking of their loss in the previous film, Tony says:
I said we'd lose. You said, 'We'll do that together too'. Guess what, Cap? We lost, and you weren't there. But that's what we do, right? Our best work after the fact? What are— the A-vengers? We're the A-vengers, not the Pre-vengers, right?"
Besides the obvious, the victory of Thanos, what is Iron Man referencing here? When have they done their best work "after the fact" of a villain's victory? In the first film, they defeated Loki before he could take over the world, and even New York seems to have taken only modest damage during the battle, seeing how quickly everything was rebuilt. In the second, they stopped Ultron before he could carry out his plan of destroying all life. In neither of these cases did they achieve victory after the villain won.
So what is the "best work" that the Avengers do "after the fact"?