For me it's the power of systematic refactoring. A friend of mine back at H.P. used to joke: "Programming is simple. Start with the null program, and debug it

For me it's the power of systematic refactoring. A friend of mine back at H.P. used to joke: "Programming is simple. Start with the null program, and debug it until it does what you want." But seriously, I've gotten a lot of mileage from the technique of refactoring a body of code through a long series of individually simple steps, each of which either preserves behavior exactly or alters it in a predictable way.