"Why do we separate out the green step from the refactoring step? Why do you make it work, not really worrying about the code quality, and you are then cleaning by refactoring?
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Kent would say, "when you're adding new functionality to the code, you're thinking in a different mindset than when your refactoring" Refactoring, strictly defined, is changing the way the code is organized, but without actually changing its observable behavior.
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It's easier to think of only doing one thing at a time.
Switching your mentality lets you switch to thinking about code maintainability in the future without having to think about the problem you have been trying to solve. It abstracts away the problem solving much in the way a well designed class abstracts away a problem once you've moved from writing it to simply consuming its public API.
You can use tools when in this mode, like project-suture