Yeah good luck with that.

Problem is, time is just _one_ variable. It's possible to hit every estimate spot-on, if you allow the other variables to change wildly (number of bugs, completeness of features etc). It's kind of like in quantum mechanics, where by knowing one property of a particle, you have to let go of all the others (maybe).

Anyway, I blogged about this a lot here, if it is any use: https://riskfirst.org/Estimates

It seems wrong-headed to be insisting on this, so maybe education is the answer?