Why estimation is wrong and will hurt you ?
1- Starting with All Our Requirements Is Wrong:
At the very beginning, we know less about our project than we’ll ever know again.
2- Estimating When We’ll Be Done Is Wrong; Forcing the Answer Is Worse:
Developers too, know less about this product than they ever will again, and they don’t understand most of these requirements very well.
3- Agile Teams Work in Short Iterations; They Pick an Amount of Work that They Forecast They Can Accomplish:
If a team has more work thrust upon it than they think they can accomplish, they generally fall short.
4- Having Demanded the Impossible, Management Asks for Better Estimates: