YAGNI battles the Black Swans

There's been a lot of fuss in the economic world about a book called The Black Swan: The Impact of the Highly Improbable by Allen Lane. Lane uses the metaphor of the discovery of the Black Swan to explain his theory: basically before the discovery of Australia people believed there were only white swans in the world and created a whole set of theories around this 'fact'. Then a black swan was discovered in Australia junking the theories.

Using this as a template Lane defines a Blank Swan as a highly improbable event with three principle characteristics: it is unpredictable; it carries a massive impact; and, after the fact, we concoct an explanation that makes it appear less random and more predictable than it was.

Lane goes onto criticize businesses, markets and politicians for their over confidence in prediction. Lane even goes to the extent to suggest that it is a cold, hard fact that we cannot predict Black Swans but by preempting the future based on our belief that only White Swans exist we set ourselves up for disaster. So when a Black Swan does come along - and Lane argues that they come up a lot more than we predict - we've made things a whole lot worse by planning around White Swans.

Any developer who's every used the phrase "You Ain't Gonna Need It" would identify with Lane's theory. YAGNI tell's us that we should only implement what we need not what we foresee we need - no matter how sure you are that you're gonna need it. By writing code which preempts the future design we are building systems for White Swans and when that Black Swan comes along (and it will) we're going to be running around trying to refactor a load of over-engineered code. The difference between a Black Swan developer and a White Swan developer is the Black Swan developer accepts this and uses YAGNI to battle it where as a White Swan developer just re-engineers his predictions by turning the latest Black Swan into another White Swan - that is until the next Black Swan rears it's ugly head.

I think YAGNI developers - either naturally or through experience - think that life is full of Black Swans. I think that this is why some developers don't get YAGNI: they only believe in white ones. Maybe a different approach is not to say to them "You ain't gonna need it" but maybe say "Black Swan".