David's Blague

Inspired by Mark Jason Dominus, my short description of Gödel's first incompleteness theorem:

No set of rules is both consistent and complete.

For favorite long(er) explanations, see the appendix to Rudy Rucker's Infinity and the Mind or Nagel and Newman's Godel's Proof.  If you read the latter, read the one edited by Douglas Hofstadter, who is awesome.