Brooks’ law – Mythical Man-Month


I recently finished reading the book “The Mythical Man-Month”. This book was written by Frederick Brooks Jr. and first published in 1975. This book has been quoted as “the Bible of Software Engineering.” It is based on the experiences of the author at IBM while managing the development of OS/360.

Although the topic of the book is software engineering, I believe that the principles identified in the book are applicable to any project.

The main idea of the book is about the mythical man-month which may be intuitive to some people. This basically can be explained as follows;

  • Project cost is proportional to the number of people involved. Cost = number of men * number of months.
  • Project progress is not proportional to the number of people involved. Number of men or people and months are not interchangeable.

Brooks says “Man-month as a unit for measuring the size of the job is a dangerous and deceptive myth.

This book also gave us Brook’s law. Brook’s law can be stated as follows;

“Adding manpower to a late software project makes it later.”

There is some resemblance to Braess’ paradox in traffic networks, which can be loosely stated as “Adding extra capacity to a network in some cases brings down the overall performance of the network”. I will discuss more about Braess’ paradox at a later time.

Brooks’ Law:

There are multiple factors that make Brook’s law work. The first is the amount of time needed for a new member to get accustomed to the project. This is treated as “ramp-up” time. The second factor is communication. As more members are added to a team, the complexity of communication requirements increases. This is referred to as communication overhead. The third factor is the project type. If there are sequential tasks that are independent in nature, this results in delays due to the first two factors. When a task cannot be partitioned because of sequential constraints, the application of more effort has no effect on the schedule. In Brooks’ words; “The bearing of a child takes nine months, no matter how many women are assigned.”

Why Did the Tower of Babel Fall?

This is perhaps the section that I enjoyed the most. Brooks performs a “management audit” on the Babel project. The tower of Babel is a famous story in Bible, in the book of Genesis. The people of the world wanted to build a tower that reached to the heavens. In the story, the people spoke only one language, and God made the people speak in different languages so that they could not understand each other, and the tower was never completed.

Brooks reviewed the following factors for the “Babel Project”;

A clear mission: There was a clear mission – to build the tower.

Manpower: There was plenty of manpower.

Materials: Clay and asphalt were abundant.

Time: There was no time constraint noted in the story.

Technology: The technology available at that time was adequate.

The Tower of Babel was never built because of two reasons – communication and organization. Brooks explains that lack of effective communication led to lack of coordination. When coordination failed, the project came to a halt. In today’s world, lack of effective communication is very relevant. In my view, the point of organization is about system optimization. Pursuit of local optimization will always result in a decrease of system performance.

I highly encourage the reader to read the Mythical Man-Month book. The first edition is available electronically here.

Funny Project Management Story:

I will end with a story I heard about project management.

A man is flying in a hot air balloon and realizes he is lost. He reduces height and spots a man down below. He lowers the balloon further and shouts:

“Excuse me, can you help me? I promised my friend, I would meet him half an hour ago, but I don’t know where I am.”

The man below says, “Yes, you are in a hot air balloon, hovering approximately 30 feet above this field. You are between 40 and 42 degrees North latitude, and between 58 and 60 degrees West longitude.”

“You must be an Engineer,” says the balloonist.

“I am,” replies the man. “How did you know?”

“Well,” says the balloonist, “everything you have told me is technically correct, but I have no idea what to make of your information, and the fact is I am still lost.”

The man below says, “You must be a project manager”

“I am,” replies the balloonist, “but how did you know?”

“Well,” says the man, “you don’t know where you are or where you are going. You have made a promise which you have no idea how to keep, and you expect me to solve your problem. The fact is you are in the exact same position you were in before we met, but now it is somehow my fault.”

Always keep on learning…

In case you missed it, my last post was about “The Mystery of Missing Advent Calendar Chocolates”.