TDD is a tradeoff. TDD improves good design *for the user* at the expense of implementation design *for the coder*. Because you write how the code is going to

TDD is a tradeoff. TDD improves good design *for the user* at the expense of implementation design *for the coder*. Because you write how the code is going to be used first, you're completely free of implementation constraints, so you can make it as easy as possible for the user to use your library/app/whatever. This makes it harder for you because now you have implementation constraints that you didn't necessarily have if you started without TDD. That's the whole point of TDD.