If testing costs more than not testing, then don't test.
If you're having trouble succeeding, fail.
Testing is not the point. The point is about responsibility.
Listening, Testing, Coding, Designing. That's all there is to software. Anyone who tells you different is selling something.
I'm not a great programmer; I'm just a good programmer with great habits.
I tell people to start implementing when they are pretty sure there aren't more important stories out there. An iteration's worth of data is worth months of speculation.