He messed up a mission as early as Cheeseburger Backpack (the third episode) -- the Gems aren't particularly hard on him about it, but we find out later that they have plot-based reasons for that.
There are a bunch of episodes where the point is for him to learn a Valuable Lesson. From the first season, Future Vision, Winter Forecast, Secret Team, and Open Book all count.
And there are plenty where he messes up or needs to be saved at some point throughout the story. Serious Steven, Joking Victim, and Steven the Sword Fighter all have some of this.
He gets a lot better at being smart and thoughtful over the course of the series. It's honestly some really satisfying character development to watch.
Re: Spoiler warning for season 3
There are a bunch of episodes where the point is for him to learn a Valuable Lesson. From the first season, Future Vision, Winter Forecast, Secret Team, and Open Book all count.
And there are plenty where he messes up or needs to be saved at some point throughout the story. Serious Steven, Joking Victim, and Steven the Sword Fighter all have some of this.
He gets a lot better at being smart and thoughtful over the course of the series. It's honestly some really satisfying character development to watch.