Personal Calibration
When I say I’m 80% sure I will have that project done by Friday, what do I mean by that? What I should mean is that in 8 out of 10 similar situations I would be done by Friday and in 2 out of 10 I would not.
In reality people are frequently miscalibrated. When they say 80% it may in fact turn out that only in 5 out of 10 similar projects they would be done by the predicted date.