Sharks are predators and will usually only follow through on an attack if they have the advantage, So making the shark unsure of its advantage in any way possible will increase your chances of survival Contrary to popular opinion, the shark's nose is not the area to attack, unless you cannot reach the eyes or gills. Hitting the shark simply tells it that you are not defenseless. If a shark shows itself to you, it might just be curious and may swim on and leave you alone. If you are under the surface and lucky enough to see an attacking shark then you do have a good chance of defending yourself if the shark is not too large.