They all have regrets.
Tony wishes he could've been the perfect son; he'll never accept that there is no such thing.
Steve wishes he could've saved Bucky and had the dance with Peggy; then he realises that he was needed more in a different era.
Bruce wishes he never turned into it; he could've had so much.
Clint and Natasha wish they could admit their feelings; it's too hard, too much effort, and they're both afraid of what happens next.
Thor wishes he had his brother back.