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

Brooks drew on IBMInternational Business Machines — a major computer and enterprise technology company since the early 20th century. OSOperating system — software that manages hardware and provides services to applications./360 experience: onboarding and communication overhead eat the calendar. The line is still cited in sprint planning, reorgs, and every thread about 'we just need more engineers.'

Brooks's Law outlived the OSOperating system — software that manages hardware and provides services to applications./360 project it described.

It gave managers vocabulary for why throwing bodies at schedule risk backfires.