Brooks' law

Adding manpower to a late software project makes it later

Brooks himself has called this law an 'outrageous oversimplification'.

The main factors of why:

It takes time for the people added to a project to become productive, to ramp up. Established workers have their productivity diminished by brining new workers up to speed.
- New workers may even make negative contributions, slowing the project down
Communication overhead increases as the number of people increases
Adding more people to a highly divisible task does help, but some tasks are not divisible. Nine women can't make a baby in a month.