4. Iron Man's Condition & Retirement - Iron Man / Iron Man 3
Iron Man 3 ended with Tony Stark having his arc reactor removed from his chest and retiring from superhero activities indefinitely. This meant that audiences had been misled on two fronts - the first being that, in the first Iron Man movie, they'd been led to believe that the arc reactor was essential for Stark's survival, could not be removed and was now essentially a part of him, and the second being that he hasn't actually retired at all, given that he's set to don the Iron Man armour in Avengers: Age of Ultron and a number of subsequent films after that one. Things like that make seemingly big moments and key plot points seem pointless and are a sure-fire way to anger fans. Had it been so simple to remove the arc reactor, why didn't Stark do it sooner? And if Marvel knew Stark wasn't actually going to to retire Iron Man at all, why have the character make such a big gesture?
