The CAP Theorem
A system spread across several machines can give you consistent answers, or always answer at all. The network makes you choose.
2000 (conjectured), 2002 (proved)23 min read
American computer science
Eric Brewer
American computer scientist, professor at UC Berkeley and later a vice president at Google. He built some of the first large clustered web services at Inktomi, and in a 2000 keynote to the ACM Symposium on Principles of Distributed Computing proposed the conjecture that consistency, availability and partition tolerance cannot all be had at once. Twelve years later he wrote a widely read correction of how his own conjecture had come to be misused.