You may have the newest DSLR or the fastest lenses known to man, but without even a basic understanding of light, it is going to be an uphill battle to create the images you envision. While this tutorial is directed primarily toward animators, the ideas and concepts within it are applicable to anyone who wants a better understanding of some basic lighting fundamentals.
In the video, Andrew Price mentions that humans have a natural bias towards top-down lighting. This is due to the fact that we live on Earth and our main light source is the Sun. We are just hardwired to understand that light comes from above. This is the same reason that when you shine a flashlight up at your face from under your chin, you end up with that spooky look. This idea of top-down lighting in art is nothing new.
“In a survey of over two hundred paintings taken from the Louvre, the Prado, and the Norton Simon Museums, more than 75 percent were lit from the top left.” - Universal Principles of Design
My key light (which is sometimes my only light) is placed on whichever side of the camera that best suits the scene. When shooting a portrait, I start by directing the subject to turn to the side. Most people will naturally turn to a side they feel most comfortable with, and in doing so decide which side of the frame my key light is going to go on.
I want to stress that while the concepts and methods within the video are great tools to guide you when creating your images, they are by no means absolute rules. Not every image will benefit from a three-point light setup, and some setups might need to be lit solely from below. It is up to you to utilize light in a way that makes sense for the images you want to create, and learning the fundamentals of lighting is a great way to develop solid techniques and an appreciation for the process.