Ever wonder how that last rap artist you listened to managed to cover his body with tattoos and live to tell the tale after the pain of your first tattoo? The answer lies in a psychological concept known as sensory adaptation. Sensory adaptation means that activation is greatest when a stimulus is first detected. Sure, that first tattoo hurt, but as one gets more and more tattoos, their absolute threshold level, or the lowest level of a stimulus needed for the nervous system to detect a change 50 percent of the time, is increased. So by the time Wiz Khalifa or Lil' Wayne was getting their latest tattoo, they barely felt a thing.