In 2001 Jeff drew the simple diagram below on a napkin to illustrate Amazon’s virtuous cycle, also called the “Amazon flywheel.” This sketch, inspired by the flywheel concept in Jim Collins’s book Good to Great, is a model of how a set of controllable input metrics drives a single key output metric—in this case, growth. In this closed-loop system, as you inject energy into any one element, or all of them, the flywheel spins faster:
