I want to talk about the factorial function. It might seem an arcane piece of mathematics but it is valuable because it provides a way to measure the chaos that ordinary daily life can so easily turn into. Specifically, if you have a certain number of things to do, the factorial function tells you how many choices you have for the order you can do them in. Obviously, the question of sequence is only one aspect of the complexity that comes when you have many things, and it is not necessarily the most important question, but it is close enough, and it is a simple way to look at it mathematically. The factorial function shows you the way complexity grows when there are more things going on. The growth of complexity is faster than people intuitively expect, and the factorial function shows this to you.