Brooks's Law

Adding manpower to a late software project makes it later. Effort (measured in person-months) and progress (measured in time) are not interchangeable, because tasks have sequential constraints and new people add training and communication overhead before they add output.

Why it Matters

It demolishes the assumption that schedule and staff trade off linearly. New members must be trained, which pulls experienced people off the work, and communication paths grow combinatorially, so beyond a point adding people slows the project down.

Signals

• A slipping project met by adding headcount.
• Onboarding consuming the team that is already behind.
• Coordination meetings multiplying as the team grows.

Benefits

Realistic scheduling, smaller teams, partitioning work to limit communication, and adding people early rather than late, if at all.

Risks

Treating people and time as fungible; "throwing bodies" at a deadline; ignoring the ramp-up and communication cost of each addition.

Tensions

Some work can be parallelized with more people, but sequential and communication-bound work cannot; knowing which is which is the judgment.

Examples

A two-month-late project given five new engineers that ships even later as the team trains them; partitionable work such as independent modules scaling with people while a tightly coupled core does not.