The value of metaphors should not be underestimated. Metaphors have the virtue of an expected behavior that is understood by all. Unnecessary communi… - Fernando J. Corbató

The computer field is intoxicated with change. We have seen galloping growth over a period of four decades and it still does not seem to be slowing down. The field is not mature yet and already it accounts for a significant percentage of the Gross National Product.

Systems with unknown behavioral properties require the implementation of iterations which are intrinsic to the design process but which are normally hidden from view. Certainly when a solution to a well-understood problem is synthesized, weak designs are mentally rejected by a competent designer in a matter of moments. On larger or more complicated efforts, alternative designs must be explicitly and iteratively implemented. The designers perhaps out of vanity, often are at pains to hide the many versions which were abandoned and if absolute failure occurs, of course one hears nothing. Thus the topic of design iteration is rarely discussed. Perhaps we should not be surprised to see this phenomenon with software, for it is a rare author indeed who publicizes the amount of editing or the number of drafts he took to produce a manuscript.

One is faced with a dilemma: If one places total trust in all other users, one is vulnerable to the antisocial behavior of any malicious user—consider the case of viruses. But if one tries to be totally reclusive and isolated, one is not only bored, but one's information universe will cease to grow and be enhanced by interaction with others. The result is that most of us operate in a complicated trade-off zone with various arrangements of trust and security mechanisms.