In Endgame, Tony hits Steve with this head on in the beginning of the film, cursing his optimism since they have now lost. But there ends up being something insightful in Cap’s good intentions to “keep on keepin’ on” that shine brightly in this movie most of all. He is the rock of the squad who believes in Ant-Man’s idea, then recruits Tony and the rest of the team, yes with Black Widow at his side, but without him everyone (even her) was starting to give up.