Most software that is costed (before it is started) is deliberately underquoted because if the developer gave a realistic figure nobody would put up the money. That is a major reason for cost overruns. Nothing to do with poor or inadequate management! It is easy to get software 90% working, very hard indeed to get it 99% working and virtually impossible to get it 100% working even if you're Microsoft. . . .

http://ieeexplore.ieee.org/abstract/document/6349494/

Thanks very interesting article