This morning I noticed a copy of the good old Cone of Uncertainty on the wall of a cubicle at a client’s office. It reminded me of Laurent Bossavit’s ebook-in-progress, The Leprechauns of Software Engineering, in which he challenges several of the myths or assumptions that have become traditional lore in the software industry, including that one.
What is odd, to any experienced software engineer, is that the Cone diagram is symmetrical, meaning that it is equally possible for an early estimate to be an over-estimate or an underestimate. This does not really square with widespread experience of software projects, which are much more often late than they are early.
Er…wait a second. Isn’t that very assertion an example of “anecdotal evidence?” Is it another Leprechaun? Who says projects are more often late than early?
Silly Dave! Everyone knows who said that. It was the Standish Group, in their famous Chaos Report of 1994. Slightly more than 70% of IT projects fail. That’s why every office building in the industrialized world is on fire, and white-collar refugees are streaming from the cities, leaving their belongings behind except for whatever personal electronic devices they can carry.