Gilbs Laws Of Unreliability: 1) At the source of every error which is blamed on the computer you will find at least two human errors, including the error of blaming it on the computer. 2) Any system which depends on human reliability is unreliable. 3) Udetectable errors are infinite in variety, in contrast to detectable errors, which by definition are limited. 4) Investment in reliability will increase until it exceeds the probable cost of errors, or until someone insists on getting some useful work done.