Fisher's Fundamental Theorem states — in terms appropriate to the present context — that the better adapted a system is to a particular environment, … - Gerald M. Weinberg

Human knowledge is by necessity incomplete. We cannot know in advance what we might be able to know and what might be essentially unknowable. But of one thing we can be sure: if we do not try to find things out, we shall never succeed.

Or, suppose you want to motivate your managers to ship products on time, so you conspicuously promote each manager whose product goes out the door on schedule. All goes as planned until the situation arises in which one of your managers has a project where the testers are reporting numerous problems. Because managers who have shipped products on time have been promoted, this manager thinks, I want that promotion so I need to ship this on time, but those bug reports are getting in the way. I know what I'll do! I'll put the testers on another project until the developers have a chance to catch up.

Systems are complex. A computer system is not just hardware, not just software, not even just people plus hardware plus software. The procedures, formal and informal, that have evolved with the system are part of the system; so is the current load on various components, and so is the attitude and experience of the users. Even among the commonly accepted “parts” of a system, clear lines of separation do not exist. Hardware merges with operating system, operating system merges with programming language, programming language merges with debugging tools, debugging tools merge with documentation, and documentation merges with training, and all of them mingle with the social climate in which the system is used.