@Kevinjohn Gallagher

The Mythical Man-Month - 1975

And when Brooks wrote this, it was not new or penetrating insight. It had been plain for many years.

Planning software creation is extremely fraught, and counterproductive. Getting excited and trying to cajole the process, is herding cats.
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No, seriously. The recent-years tendency to view scheduled release cycles and timed production goals as realistic & rational practice is the aberration ... not that these efforts don't work.

The truth about 'planning' software production, is that soas not to consistently embarrass oneself, generous 'padding' must be built into the projection. Both time & cost will be saved, by accepting that it will be done when it's done.