Most systems are complex. The design and development of a complex system involves many participants from various specialties. Systems engineers, in particular, specialize in those issues that have to do with the effectiveness of the whole system . In the city, for example, the automobile-transportation system competes with one or more public transportation systems such as taxis and urban mass transit. On a smaller scale, the automobiles of one manufacturer compete with those of another manufacturer.
All product designs require iteration.
Unforeseen consequences or side effects always appear when a new product is used. These consequences demand modifications to the product. Complex systems are composed of parts and subsystems, each of which undergoes iteration in its design and development. In addition, there are mismatches between the initial subsystem designs, owing primarily to inadequate understanding by subsystem designers of the workings of the larger system. This limited view leads to unnecessary iteration in the design and development processes.