40 CHAPTER 1 Systems impact in mind at all times. The bottom line is that a computer system designer's most potent weapon against complexity is the ability to say, "No. This will make it too complicated." As we proceed to study specific computer system engineering topics, we shall make much use of a particular kind of simplicity, to the extent that it is yet another design principle: adopt sweeping simplifications So you can see what you are doing. Each topic area will explicitly introduce one or more sweeping simplifications. The reason is that they allow the designer to make compelling arguments for correct- ness, they make detail irrelevant, and they make clear to all participants exactly what is going on. They will turn out to be one of our best hopes for keeping control of complexity.