Systems that meet relatively small numbers of requirements will usually give people most of what they need. (If not most of what they want.) But people, many of whom should know better, insist on having it all, and thus doom themselves to building systems that fail. Either the systems are built and do not perform to expectations, or they never get finished. Why is this so, and how can people be brought to appreciate the “requirements trap”? The problem exists because: Full article
Evaluation Uncertainty 
Sir,
The article on system design :Requirements,complexity and cost is good enough to give a start up idea of system design in terms of requirements complexity and cost.Thanks a lot..Generally in system design requirements evolve from the initial phase of identifying the clients needs and it gradually get developed only after passing through different stages of feasibility analysis,technical performance measure etc.During this stages the design optimization is gradually attained through feedback loops.Hence the cost factor can be reduced to a large extend if the system design requirements is configured properly.