There are only two hard things in Computer Science: cache invalidation and naming things. -- Phil Karlton

Long a favorite saying of mine, one for which I couldn't find a satisfactory URL.

Like many good phrase, it's had a host of riffs on it. A couple of them I feel are worth adding to the page

There are 2 hard problems in computer science: cache invalidation, naming things, and off-by-1 errors. -- Leon Bambrick

There are only two hard problems in distributed systems: 2. Exactly-once delivery 1. Guaranteed order of messages 2. Exactly-once delivery -- Mathias Verraes

there's two hard problems in computer science: we only have one joke and it's not funny. -- Phillip Scott Bowden

The first place anyone found it on the internet was in Tim Bray's blog. Tim said that he first heard it around 1996-7

Revisions 2009-07-14: original post 2010-12-21: added off-by-one variation (unattributed) 2015-08-14: added distributed tweet 2017-03-30: added proper tweet for off-by-one and mention of Tim Bray's source 2017-12-22: added the Phillip Scott Bowden tweet