No matter what kind of picture you are trying to take, either a portrait, or a landscape, or a car, or a cat, or a nude girl.

No matter if it is, in a studio, in the street, on the top of a mountain or under water.

It could be a flash, two flashes, more flashes, the sun, the moon, some lamps, some fire, or even a small thing in the eye of your model.

But to make a nice picture, never forget that.