Why are TV detectives always sad?

Vulture

"If the premise of a TV show is that a detective searches for justice, it follows that the detective will be almost unbearably sad," says Kathryn VanArendonk. "Her ability to do her job will occasionally be hindered by her alcoholism, or her post-traumatic stress, or her grief. A scene depicting professional competence will come hand in hand with a scene where the detective walks into his sad lonely apartment and eats out of a can while hunched on a mattress sitting on the floor. Searches for social justice are fueled by the need for personal vengeance. It’s so common, it’s now difficult to even imagine a happy detective."