Model: Brooks law

adding new people to a project doesn't immediately increase its capacity

in fact, it quite possibly reduces capacity during an initial stage

ramp-up period necessary to bring people up to speed,

communication lines inside the team also increase significantly with every new member.

emotional adaptation required both from new and old team member

(the storming stage of Model: Tuckman's Performance Model)

(origin: Book: The Mythical Man-Month - Frederick Brooks)

(src: Book: Team Topologies - Matthew Skelton & Manuel Pais)

ref: https://en.wikipedia.org/wiki/Brooks%27s_law