I distinctly remember one occasion when I was instructing a group of software engineers on the topic of "agile planning", and I started drawing a picture of the "cone of uncertainty".

And I stopped dead in my tracks.

Because I'd just realized I hadn't the foggiest idea what I was talking about, or how I'd know if it made sense. I was just parroting something I'd read somewhere, and for once trying to explain it wasn't helping me understand it better, it was just making me confused. And all I wanted to say anyway was "don't trust estimates made at the beginning of a project".

Fortunately nobody noticed (that often happens, and is a topic in its own right), I moved on, stopped using that picture and mostly forgot about it.

This was a few years back, and I like to think that in the meantime I've traversed the valley that lies behind Mt Stupid, and am now ready to start talking about it again. In particular what scares me - you'll be scared too if you google for "software" and "cone of uncertainty" - is how many people in the profession are still stuck on the summit: willing to opine at length about the Cone, without an inch of critical distance from what they're quoting. Is it conceptual, speculative, empirical; if the latter, how well supported? People quoting it don't know and don't care.