I figure any phrase that people deem to be a "law" and find important enough to attribute to a specific person (even if incorrectly) probably contains some real wisdom. Here's a collection of Eponymous Laws from Wikipedia, all of which I have found to be true in my own experience.
Amara's Law: We tend to overestimate the effect of a technology in the short run and underestimate the effect in the long run.
Conway's Law: Any organization that designs a system will inevitably produce a design whose structure is a copy of the organization's communication structure.
A complex system that works is invariably found to have evolved from a simple system that worked. The inverse proposition also appears to be true: A complex system designed from scratch never works and cannot be made to work. You have to start over, beginning with a working simple system.
Parkinson's law: Work expands so as to fill the time available for its completion.
Law of the Instrument or Maslow's Golden Hammer: It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail.
Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law. (I've also heard this restated as "Every task takes longer and costs more than originally estimated.")
Occam's razor – "Entia non sunt multiplicanda praeter necessitatem." Literally, entities are not to be multiplied without necessity. When two explanations are offered for a phenomenon, the simplest full explanation is preferable. (Or in modern terms: Keep It Simple, Stupid!)
Pareto principle – 80% of consequences stem from 20% of the causes.
Schneier's law – Any person can invent a security system so clever that she or he can't think of how to break it.
Sturgeon's law – Ninety percent of everything is crap.