One of the most important aspects of software development is isolation. We use many different forms of isolation. Labels in assembly language isolate jump targets from the jump instructions so that additional code can be added without having to fix all of the jumps. Subroutines isolate common operations. Local variables have an isolated scope. Classes isolate data and operations from other data and operations. Usually when we isolate one component of software development from another, the system becomes easier to develop. The impact of changes becomes easier to analyze and it makes it possible to have some confidence that a change will have only the effect the developer wants it to have. In fact, I would say that it's isolation that makes software development possible.
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