Though copious errors guarantee worthlessness, zero errors says nothing about the value of software. This is Gerald Weinberg's "Absence of Errors Fallacy." It really puts testing into perspective. It also puts all software engineering and management into perspective. The first part of the principle is obviously true; software with many errors is useless. The second part provides food for thought. It says that, no matter how hard you work to remove errors, you are wasting your time unless you are building the right system. Akao's Quality Function Deployment provides details on one method of ensuring that you are building the right system throughout the live cycle. A corollary to this principle is that all the formal methods, all the testing, and all the product assurance in the world won't help if you are building the wrong system.
Reference:
Weinberg, G., Quality Software Management, Vol. 1: Systems Thinking, New York: Dorset House, 1992.
