Speaking of dead as a doornail, hair products, like shampoo and conditioner are mostly useless and cannot physically change your hair. The hair that is visible on the human body is dead hair and live hair is beneath the surface of the skin. Nothing you add to the visible hair can actually make it healthier. Also, no hair products can repair split ends.
Some hair products may add the artificial appearance of shine or
color and for most, that is sufficient.