By Herb Simon
The engineer, and more generally the designer, is concerned with how things ought to be—how they ought to be in order to attain goals, and to function.
The research that was done to design computer time-sharing systems is a good example of the study of computer behavior as an empirical phenomenon. Only fragments of theory were available to guide the design of a time-sharing system or to predict how a system of a specified design would actually behave in an environment of users who placed their several demands upon it. Most actual designs turned out initially to exhibit serious deficiencies, and most predictions of performance were startlingly inaccurate.
Under these circumstances ==the main route open to the development and improvement of time-sharing systems was to build them and see how they behaved==. And this is what was done.