Agreed. The problem is that software really falls into 2 main categories: 1) doing something that has already been done in a very similar way. This type of sof

Agreed. The problem is that software really falls into 2 main categories: 1) doing something that has already been done in a very similar way. This type of software is relatively predictable and estimates are generally reliable, assuming that is being done by the same team that worked on the prior implementations. 2) doing something new where NO ONE actually knows what the specification really is or how hard it will be to implement. Most of the time, people don't even know who all the constituencies that will have opinions or requirements to contribute to the specification. Estimating this type of work is largely a guess in the dark, and there are no reliable ways of producing valid estimates, so it is all based on prior interactions with the group and experience of the senior developers with this type of project. Most managers think they are in camp 1), but in practice if that was true they'd just buy off the shelf software. You're doing your own because something is different.