1.1 Systems and Complexity 3 design of cities), mechanical engineering (automobiles and air conditioning), aviation and space flight, electrical engineering, and even ecology and political science. We start by looking at some of those common problems. Then we will examine two ways in which computer systems pose problems that are quite different. Don't worry if some of the examples are of things you have never encountered or are only dimly aware of. The sole purpose of the examples is to illustrate the range of considerations and similarities across different kinds of systems. As we proceed in this chapter and throughout the book, we shall point out a series of system design principles, which are rules of thumb that usually apply to a diverse range of situations. Design principles are not immutable laws, but rather guidelines that capture wisdom and experience and that can help a designer avoid making mis- takes. The astute reader will quickly realize that sometimes a tension, even to the point of contradiction, exists between different design principles. Nevertheless, if a designer finds that he or she is violating a design principle, it is a good idea to review the situ- ation carefully. At the first encounter of a design principle, the text displays it prominently. Here is an example, found on page 16.