The atlantic has a great article about "the management myth" in is archive. Don't read it if you are taking things to serious. I pretty much like the main statement written between the letters since I am a big fan of non violent communication and also a great believer in "everyone is different".
If you don't want to read the whole story, you can go on with my summary.
- If you need to add a buffer of more than five percent, you should stop wasting your time trying to measure and plan things since it is obvious you are either trying something impossible. Listen to your gut, it is as precise as a five day thread workshop.
- If you really want to measure a regular task, do not choose your best horse, simple record things a week or two and use this as numbers of truth. If you don't like the numbers, never ever try to "optimize" them.
- If you don't like the numbers after a forecast or threat analysis, don't try to "optimize" them.
- Management is more about people than about optimizing work.
- People are different, each to another and the same compared over a period of time.
- Instead of pushing single channeled communication, try to have dialogues (that thing where the other side and you could be right in the same time ).