Mastery of system dynamics gives one a variety of ways to be useful and earn a living. Since my first course in Industrial Dynamics at MIT in the fall of 1964, I have used SD in five careers: teacher, author, consultant, manager, and investor. These careers require different levels of mastery. They offer different possibilities for impact. And each has its own risks. I will describe each of these roles briefly and indicate the benefits and costs that confront anyone wishing to pursue that career.