The mythical man month

If a certain job can be completed by 10 people in 4 days, then the same job can be completed by 20 people in 2 days.
Thus, the unit of work representing the productive effort of one person in one month is called a man month.
So if you add more man power at any point of time during the project life cycle, you can expect that the task is completed earlier.
This applies as a general principle across industries. The software industry oh being an exception.
Some of the myths in software industry are:
You can increase the overall productivity by adding more man man power
You can add man power at any point of tome in the project
By adding more man power, you can execute the project earlier.
Programmers are more efficient under pressure.
More man months means accurate program.
The bottom line is in software engineering, the man months are not directly proportional to the productivity.
A program, however small needs to be maintained one day.
A well written program is a heaven in itself; a badly written program is a hell.