Pain, whether expressed or held in, gives an NPC depth.
Please take a look at the art. In this hypothetical game, you're a captain on a distant planet a space outpost accompanied by your Lieutenant. In this moment of the game, just before you arrived, an alien ship landed. The Lieutenant panicked and blasted the ship, killing the two innocent and peaceful aliens on board who were merely trying to escape. There's one survivor, a female alien.
You and your Lieutenant didn't expect to encounter an alien ship on this outpost. He's still freaked out and is about to kill the woman. So now find yourself in a potential firefight with your own partner.
The female alien is devastated. Those closest to her have just been murdered by your right-hand man.
Her pain gives her depth.