Random numbers should not be generated with a method chosen at random

TeX has found at least one bug in every Pascal compiler it's been run on, I think, and at least two in every C compiler

Programs are meant to be read by humans and only incidentally for computers to execute.

An algorithm must be seen to be believed.

Always remember, however, that there’s usually a simpler and better way to do something than the first way that pops into your head.

These machines have no common sense; they have not yet learned to "think," and they do exactly as they are told, no more and no less. This fact is the hardest concept to grasp when one first tries to use a computer.

...One of the most important lessons, perhaps, is the fact that SOFTWARE IS HARD. From now on I shall have significantly greater respect for every successful software tool that I encounter. During the past decade I was surprised to learn that the writing of programs for TeX and Metafont proved to be much more difficult than all the other things I had done (like proving theorems or writing books). The creation of good software demand a significiantly higher standard of accuracy than those other things do, and it requires a longer attention span than other intellectual tasks.