The World Is Complicated. Get Used To It.
Joel provides an excellent example of real world design trade-offs in a recent post.

"Design is all about making hard choices and, hopefully, sometimes, hitting upon elegant solutions that solve conflicting goals. But when you can't solve conflicting goals, you have to be smart enough to decide which goal to solve, and not just be a lazy punter and pretend that adding a checkbox to the options dialog will solve it."