Thats the thing though, he didn't fail accidentally unlike before, he chose to fail. In the end he chose to be a bystander because he could have actually stopped Eren from going into the military right then, if you remember it was keith shadis who told everyone about the broken clasp and asked Eren too were a new one, if he hadn't decided to do that and basically give him another chance with a new equitment, Eren would have failed. Keith could have completely changed the course of the story right then, he could have been "special" but he chose not too.