Because it sounds like "start with tests, design and plan never". Too often tests-first is a substitute for a thought-out architecture and data flow.

That's certainly true; but when you've done your homework, it can be a really great experience.

For example: the past 3 weeks I've been pounding out tons of code in a TDD fashion. But prior to that:

* I spent a week writing up a detailed design document and getting feedback from teammates and stakeholders.

* Another week refactoring (TRULY refactoring; no changes to functionality) the existing implementation so I can reuse the existing work in my new implementation.