In a famous physics demonstration, the professor lies down with a cinder block on her chest. Her assistant then slams the cinder block with a sledgehammer as hard as he can. Although the professor would be severely injured if she received the seldgehammeer’s blow directly, with the cinder block in place she emerges from the ordeal relatively unharmed. Why? Shouldn’t having extra weight on her increase the danger rather than mitigate it?
Sometimes this demonstration involves a bed of nails, just for extra showiness.