"Without test-first and refactoring, clients think
 they must assemble as many program requirements as
 they can afford to have written. This effort snarls
 all relative business priorities together, making
 Scope Control impossible. It obscures opportunities
 for simplification. Designing and implementing many
 features all at once is very hard, leading to our
 industry's reputation for very large failures. Putting
 tests in front of development's inner cycle permits an
 outer cycle of incremental feature growth. That
 relieves the Customer of the responsibility to predict
 the future and guess which complete set of features
 will maximize productivity."

.. Juergens answer:

 Nice description.
 Sometimes I try to explain that to non technical people
 with the following picture:

 If you have only one chance to get your wishes on a
 list, it is like Christmas for a child. You make sure
 you get every little wish on that list and hope for the best.

 If you are sure that you can get your wishes on the list
 at any time. You will just put the most important ones
 there which come to your mind easily.