"Although helmets are effective in protecting the skull from fractures, the force of the impact can still affect the brain inside the skull. Picture an egg. A concussion is like shaking an egg. As you shake an egg, the yolk (like the brain) moves around inside the shell. If you were to protect the egg by adding a helmet onto the shell, the addition of the helmet would not prevent the yolk from still moving around if you were to shake the egg,"