"Why is there never time to do it right, but always time to do it over?"

  — Anon

"It doesn't matter that the underlying code is flawless—any part of the user interface is bad if it leads reasonable people into errors, confuses them, irritates them, or provides them with too little flexibility or functionality to do a test they reasonably expect to be able to do with the product."

  — Cem Kaner et al, Testing Computer Software (1999), p 36

"Also as a consequence of the introduction of new bugs, program maintenance requires far more system testing per statement written than any other programming. Theoretically, after each fix one must run the entire batch of test cases previously run against the system, to ensure that it has not been damaged in an obscure way. In practice, such regression testing must indeed approximate this theoretical idea, and it is very costly."

  — Fred Brooks, The Mythical Man Month (p 122)