I can't tell you how many times I have to explain this to clients.  So I figured I would put up a local copy of this article so it was always on hand as a visual assistant.  Article (I believe) was originally published here.

Below is The Designers Holy Triangle! When creating a project, clients must choose only two out of the three options. They can't have it all. It's a reality of life, clients must deal with it. Web designers must deal with it.

Good + Fast = Expensive

Choose good and fast and we will postpone every other job, cancel all appointments and stay up 25-hours a day just to get your job done. But, don't expect it to be cheap.

Good + Cheap = Slow

Choose good and cheap and we will do a great job for a discounted price, but be patient until we have a free moment from paying clients.

Fast + Cheap = Inferior

Choose fast and cheap and expect an inferior job delivered on time. You truly get what you pay for, and in our opinion this is the least favorable choice of the three.