They're ninjas. They wear dark clothing and hide in the shadows, watching their enemies unseen with only their eyes exposed.
They take on missions of spying and assassination, and will die rather than reveal their affiliation or the name of their employer.
Obviously they need shiny pieces of polished metal on their foreheads which display the insignia of their secret home village.>>11182258>"As soon as I get back to the village, I'm getting married!"
Don't worry. Shikamaru has taken on all of his attributes and responsibilities, including boning his bereaved girlfriend.