Motivated lighting

The audience never analyses this consciously. They just find the picture believable or slightly off. Motivating a light means matching its direction, colour and hardness to whatever is supposedly making it, so a lamp in frame justifies warm light from that side and a window justifies cooler, softer light from that direction. Creators use it because one practical lamp in shot buys permission for a whole lighting setup. The alternative is unmotivated light, perfectly usable in stylised work, though it reads as artificial the moment a scene is meant to look like a real room.