For any given project, pick two of the above... You can't have all three.
So, in the past couple of days, we've had some discussions oabout Effort Estimates (a.k.a Effort Guesstimates) for a specific project we were discussing.
Different numbers were thrown around, mostly more than a couple of days.
This lead me to the following statement regarding Effort Estimates:
Any estimate longer than a week is at risk Any estimate longer than two weeks is unknown
This rule-of-thumb statement basically means that if you want to predict or at least estimate the required effort, you better break the effort into chunks that are less-than-or-equal-to one week chunks.
Good luck with that...