Razor's edge

Occam's Razor: Also known as the "principle of parsimony," is frequently cited as Entia non sunt multiplicanda praeter necessitatem, which translates to "entities must not be multiplied beyond necessity." Paraphrased: "of two competing theories, the simpler explanation of an entity is to be preferred," so when competing hypotheses about the same prediction have equal explanatory power, one should prefer the hypothesis that requires the fewest assumptions.

Occam's Razor also gave way to this beauty:

Hanlon's Razor: Never attribute to malice that which is adequately explained by stupidity.

Even though it was submitted to a humor book called "Murphy's Law Book Two: More Reasons Why Things Go Wrong!" it still has a lasting impact. Those who work in corporate America would tend to agree.

Variations:

Grey's Law: Any sufficiently advanced incompetence is indistinguishable from malice.

Douglas Hubbard's corollary: Never attribute to malice or stupidity that which can be explained by moderately rational individuals following incentives in a complex system.

HG Wells: There is very little deliberate wickedness in the world. The stupidity of our selfishness gives much the same results indeed, but in the ethical laboratory it shows a different nature.

Churchill: His insolence ... may be founded on stupidity rather than malice.