prototyping for fun and profit

From The Bottom-line of Prototyping and Usability Testing:

“The main reason why user-centred design techniques aren’t used in practice is that they are believed to be uneconomical, time consuming and altogether a luxury, which can be done without. But sticking to the waterfall model is like peeing in your pants. It will get back at you with expensive changes during development and major costs on re-engineering the product after launching. ”