1. Our techniques of estimating are poorly developed.
(This reflect an unvoiced assumption which is quite untrue, ie: "that all will go well" )
All programmers are optimists (because of programmer are young, optimistic, " this time it will surely run", "I just found the last bug" "that all will go well", "that each task will take only as long as it "ought" to take".
2. Our estimate technique fallaciously confuse effort with progress, hiding the assumption that men and month are interchangeable.
" the man-month as a unit for measuring the size of a job is a dangerous and deceptive myth."
" man and month are interchangeable commodities only when a task can be partitioned among many workers with no communication among them."
"when a task cannot be partitioned because of sequential constraints, the application of more effort has no effect on the schedule. The bearing of a child takes nine months, no matter how many women are assigned. Many software task have this characteristic because of the sequential nature of debugging."