The top answer to this question on Quora is the best I've seen. http://www.quora.com/Engineering-Management/Why-are-software-development-task-estimations-regula

The top answer to this question on Quora is the best I've seen. http://www.quora.com/Engineering-Management/Why-are-software-development-task-estimations-regularly-off-by-a-factor-of-2-3 http://www.quora.com/Engineering-Management/Why-are-software... What really surprises me is that everyone accepts that there have to be estimates. While estimates are useful in many scenarios, most of the estimates I see developers giving add no value and are a waste of time. I've been working with teams now for the last 2 years who don't do estimates, and they are the highest performing teams I've ever worked with and the rest of the business have the highest trust in IT I've seen.