'Avengers: Endgame' Screenwriters Reveal Why 'Iron Man 4' Would Have Been 'One Too Many'Throughout the past 11 years, the Marvel Cinematic Universe has grown into the most financially successful film series of all time. Audiences the world over have become so invested — literally and figuratively — in these characters. And that’s precisely why Avengers: Endgame felt like both a payoff and a gut punch.