Accidents happen. Sometimes important accidents happen, like Christopher Colombus discovering America, or the inventor of the popsicle leaving soda out overnight with a stick in it. Videogames are no exception, and sometimes the biggest contributions to games have been entirely unintentional.
Though many of you could not even imagine what life would be like without being able to experience a 1:1 backswing in Wii Sports Resort, golf wasn't supposed to be part of the sequel in the first place. During 2008's E3, Nintendo Superproducer Shigeru Miyamoto talked up how much better Wii golf was going to be in the new game, due to the WiiMotionPlus adapter. The development team had no choice but to put golf in, since he mentioned it in an interview. This was a maneuver that Miyamoto actually referred to as "blocking off the escape route," because that's what happens when you're the Steve Jobs of Japan.
We all live in fear of the frightening sound of Sonic's drowning theme, but it might have never happened. According to an interview with Sonic creator Yuki Naka, the reason that Sonic can't swim in water levels is because he at the time thought hedgehogs couldn't swim. It makes Labyrinth Zone even more disappointing, not just because it was really really hard, but also because it sullies what was once a realistic portrayal of the way hedgehogs curl up in a ball, run really fast, and defeat evil scientists.