Architecture & practice·Estimation and planning
three engineers joined the late project and the next month was slower than the one before.
Brooks's law
Also calledmythical man-month, adding people to a late project
Adding people to a late software project makes it later. The mechanism is onboarding and communication overhead: new people consume the time of the people who know things, and the number of communication paths grows faster than the headcount. It does not mean never add people — it means the payback period is measured in months, so growing a team is a solution to next quarter and never to this deadline.