You know: time, cost, quality. Pick any two.
But why three? And not four points?
It could be because :
- jokes use triplets
- it's the next paradigm after Dualism
- it's just a verbal construct used in marketing
This is serious because something better could be in the fog, waiting. Like an integrated cost/quality metric. Or something.
There's a rambling thread on Jason Kottke's blog about this. Numerous forgotten-their-college-philosophy types and over-reductionist engineers pull and push at the question without its centre moving very much. It's even so long it reaches repetition point, but don't let that put you off. You know: Funny, Informative, Short. Pick any two. Or something like that.