My go at it: Perhaps it means that it is impossible to create a rule that applies to a category without exception, real life is much more nuanced than that. So if you think you have such a rule, that is always valid, as people often do, we know it's a bad rule. A rule only becomes a good rule once the exception is found because that means it is a rule that has a hope of succeeding in an ever evolving real life. - Todd Hoff

Oh, and the Hacker News thread http://news.ycombinator.com/item... - Todd Hoff

Here is my go, since nobody knows what it means, don't use it. What good is an expression that everyone understands differently. There is a good deal of irony in what I am saying, but I lack the sophistication in written word to bring it out :) - Jak Sprats

I think you've just proved it Jak :-) - Todd Hoff

Good discussion of this expression on Wikipedia: http://en.wikipedia.org/wiki... - Sean McBride