Laws of Computing (circa mid-1980's)

First Law of the Computer: I am a computer. I am dumber than human, and smarter than a programmer.

Lloyde's First Law: every program contains [at least] one bug.

Eggleston's Extension Principle: Programming errors which would normally take one day to find will take five days to find if the programmer is in a hurry.

Gumperson's Lemma: The probability of a given event happening is inversely proportional to its desirability.

Weirstack's Well-Ordering principle: the data needed for yesterday's debug shot must be requested no later than noon tomorrow.

Proudfoot's Law of the Good Bet: if someone claims that you can assume the input data to be correct, ask them to promise you a dollar for every input error.

Fenster's Law of Frustration: if you write a program with no error-stops or diagnostics, you will get random numbers for your output. (This can, incidentally, be used to an advantage.) However, if you write a program with 500 error-stops or diagnostic messages, they will all occur.

The Law of the Solid Goof: In any program, the part that is most obviously beyond all need of changing is the part that is totally wrong.
Corollary A: No one you ask will see it either.
Corollary B: Anyone who stops with unsought advice will see it immediately.

Wyllie's Law: Let n be the number of last category-1 job run at the computer center, then the number of your job is either n+1 or n+900.

O'hane's Rule: The number of cards in your deck is inversely proportional to the amount of output your deck produces. [FYI: it was one line of code per card in ye olde days of programming.]

Mashey's First Law: if you lie to the assembler, it will get you.

Mashey's Second Law: if you have debugging statements in your program, the bugs will be scared away and it will work fine, but as soon as you take away the debugging statements, the bugs will come back.

The Law of Dependent Independence: It is foolhardy to assume that jiggling k will not diddle y, however unlikely.

The Law of Logical Incompatibility: all assumptions are false. This is especially true of obvious assumptions.

Velonis's First Law: the question is always more important than the answer.

Velonis's Second Law: when everything possible has gone wrong, things will probably get worse.

Velonis's Third Law: the necessity for providing an answer varies inversely with the amount of time the question can be evaded.