A more interesting/relevant article for HN would be <i>how</i> to explain this to customers. I usually sit there in sales meetings belabouring that there will be bugs, more than you expect, more than you could dream of, there will be bugs - yet when we hit UAT there's always indignant outrage that when you click X, then Y, then worship the moon on a thursday while sacrificing a goat and singing kum-bay-ya, this one figure that nobody sees is out by a tenth of a penny, and the feature that we didn't mention or even think of until Just This Moment doesn't exist.