This (quoted below) is what I was trying to say here:

4) Only the programmer who is going to write the code can schedule it. Any system where management writes a schedule and hands it off to programmers is doomed to fail. Only the programmer who is going to do the work can figure out what steps they will need to take to implement that feature. And only the programmer can estimate how long each one will take.

...

Inept managers try to address this by figuring out how to get people to work faster. This is not very realistic. ...

You might be able to get 10% more raw code out of people temporarily at the cost of having them burn out 100% in a year. Not a big gain, and it's a bit like eating your seed corn.

You might be able to get 20% more raw code out of people by begging everybody to work super hard, no matter how tired they get. Boom, debugging time doubles. An idiotic move that backfires in a splendidly karmic way.

Read more at link, above.