As per the quality of the systems, the main question is as follows: if we have all the components that are individually having high quality, will their assembly function as we want?
To understand this problem we classify and divide this problem into various types. When the components are assembled, we have one combination called WWWW. This means the system Works When We Want it to work. Similarly, the system Does not Work When we Want it to work. This combination is called DWWW. Another combination is WWDW. This system Works When we Do not Want it to work. The last combination is DWDW, the system Does not Work when we Do not Want them to work or when we do not really need it at all. This situation is not through our design, but it is only through chance event. Only WWWW and DWDW combinations are really reliable systems where we do not have any complaints about them. We want systems to be like that.
How much can we achieve this through design? How much can we battle the other two situations which are examples of unreliability and risk.