Cobra Effect · People and organisations
Brooks’s law
Adding people to a late project makes it later.
5 cards, read aloud in 1:20, with a test and sources.
Adding people to a late software project makes it later.
Fred Brooks, 1975, in The Mythical Man Month. He had just managed one of the biggest software projects in the world at IBM. It was late. They added people. It got later.
Nine women cannot make a baby in one month.
That is Brooks’s line. Some work does not divide. A month of work by one person is not the same as a day of work by thirty.
The new people have to be taught by the old ones.
Whoever knows the project stops working on it to explain it. For the first weeks the team’s output drops, at exactly the moment you needed it to rise.
And everyone has to talk to everyone.
Three people have three conversations to keep up with. Ten people have forty five. Add people and the talking grows faster than the work.
What actually helps a late project.
Cut scope. Move the date. Or accept that it is late. Adding people is the option that feels like doing something. It is usually the one that does the least.
Sources
- Brooks’s law, Wikipedia. The law, the arithmetic of the conversations, and the exceptions Brooks himself allowed. Short and precise.
- The Mythical Man-Month, Fred Brooks, 1975. The essays from the IBM project that went late. The title essay is the source of the law and of the nine women line. Half a century old and still handed to new managers.
- No Silver Bullet, Fred Brooks, 1986. Brooks’s other famous essay, on why no single invention will make software ten times easier. The same mind, a decade later, and just as right.
Nearby ideas
- Parkinson’s law. Work expands to fill the time you give it.
- Second order effects. Every fix has consequences, and those have consequences too.
- The Peter principle. Why people get promoted until they reach a job they cannot do.
- Conway’s law. Systems end up shaped like the teams that build them.
- The Hawthorne effect. Being watched changes what people do, and muddies what you measure.
- Dunbar’s number. Why groups stop working the old way once they pass about 150.
- The bystander effect. The more people who see a problem, the less each one acts.
- The fundamental attribution error. We blame people’s character and overlook their situation.