Goal Keepers in general are an odd breed. Deciding to be a goalie in the first place doesn't make much sense to me, regardless, keepers are vital to the game and the overall success of any team. For the longest time, however, I just can't seem to figure out the logic behind why keepers dive to the side on a penalty kick. Obviously they are guessing or making an attempt at picking a side the penalty taker might go, but is this really the best effort in minimizing the statistically advantage the shooter has or in maximizing the keepers chances of making a save?
Realistically, the chances are not equal to a little less than 50% because most penalty shots are placed in the green zones of the goal. So based on this logic, the keeper should pick a side to attempt to stop the shot.
If, let's say, the keeper chooses to dive to his/her right, its not just picking a side, the keeper must also choose to dive low, mid range or high. Either way, statistically speaking, the keepers chances are instantaneously reduced to around a quarter percent of a chance of making a save. At the professional level, most penalties are placed in the corner low to the ground so if a keeper were to choose to dive, dive to the middle and low to the ground.