I know this was an accident, but the results speak to the heart that the worst act in golf is to hit a golf ball at someone. It just speaks to how even though 99% of the time you don't think you can reach that par 5 in two, wait till they clear the green, that 1% could be that image above. If you don't think yelling 4 isn't important, think of that image. Even if you don't see someone there, and you know your golf ball is going towards another hole, yell 4. You don't have to see the ball heading towards someone to be considerate. With more and more golf courses getting crowded, its more important than ever to be considerate of other people, especially when a golf ball can do that much damage.