Even the best planning is not so omniscient as to get it right the first time.

Dissertations are not finished; they are abandoned.

Product procedure...must securely protect the crown jewels, but, equally important, it must eschew building high fences around the garbage cans.

The Waterfall Model is wrong and harmful; we must outgrow it.

The fundamental problem with program maintenance is that fixing a defect has a substantial (20-50 percent) chance of introducing another. So the whole process is two steps forward and one step back.

The first step toward the management of disease was replacement of demon theories and humours theories by the germ theory. That very step, the beginning of hope, in itself dashed all hopes of magical solutions. It told workers that progress would be made stepwise, at great effort, and that a persistent, unremitting care would have to be paid to a discipline of cleanliness. So it is with software engineering today.

Plan to throw one (implementation) away; you will, anyhow.