I Can’t Afford A Full-Time On-Site Customer

If you want to move at full speed, you can't afford not to have a customer onsite
full-time to answer questions for the development team. We don't know of anydevelopers have to wait for answers, two things tend to happen:
1. The project slows way down or grinds to halt while they wait, or
2. They get tired of waiting and they guess at what the requirements are.
The first result costs you money by delaying the realization of value from the
project. The second costs you money, too. Developers often guess wrong, and have
to redo lots of work. That produces still more delay.
Ask yourself a basic question: do you want the developers to give you the
software they assume you need? We suggest you save yourself the financial and
psychological pain. Put a customer at the disposal of the development team.
Better yet, ask another question. What is the alternative? A study2 recently
showed that the typical requirements document is 15% complete and 7% accurate.
That stinks! If we rely on the requirements spec, we will fail. Suppose we
accurately guess how to fill the holes 50% of the time. OK, now we are up to 57.5%
complete and 53.5% accurate. Do you feel better yet?
It is certainly true that it will often be difficult to have a customer on site or
available all of the time. Is that any reason to ignore the problem? If we do the rest
of XP, are we any worse off? We still are guessing to fill the holes.