Estimation - some people hate it, some people can't live without it. Martin Fowler said, "Estimation is neither good nor bad." Ron Jeffries said, "Estimation is Evil." Two months later he corrected himself and said, "Estimation is a necessary evil." For most people, the very essence of planning was based on estimation. And when plans went awry, the attributable root cause invariably was an incorrect estimation or the paucity of time for correct estimation.