> He didn’t say that.
Actually he did, or something very close to it.
Obviously SOMETIMES you can add more developers to a project to successfully speed it up, but Brooks point was that it can easily also have the opposite effect and slow the project down.
The main reason Brooks gives for this is the extra overhead you've just added to the project in terms of communications, management, etc. In fact increasing team size always makes the team less efficient - adds more overhead, and the question is whether the new person added adds enough value to offset or overcome this.
Most experienced developers realize this intuitively - always faster to have the smallest team of the best people possible.
Of course some projects are just so huge that a large team is unavoidable, but don't think you are going to get linear speedup by adding more people. A 20 person team will not be twice as fast as a 10 person team. This is the major point of the book, and the reason for the title "the mythical man month". The myth is that men and months can be traded off, such that a "100 man month" project that would take 10 men 10 months could therefore be accomplished in 1 month if you had a team of 100. The team of 100 may in fact take more than 10 months since you just just turned a smallish efficient team into a chaotic mess.
Adding an AI "team member" is of course a bit different to adding a human team member, but maybe not that different, and the reason is basically the same - there are negatives as well as positives to adding that new member, and it will only be a net win if the positives outweigh the negatives (extra layers of specifications/guardrails, interaction, babysitting and correction - knowing when context rot has set in and time to abort and reset, etc).
With AI, you are typically interactively "vibe coding", even if in responsible fashion with specifications and guardrails, so the "new guy" isn't working in parallel with you, but is rather taking up all your time, and now his/its prodigious code output needs reviewing by someone, unless you choose to omit that step.
>> He didn’t say that. > Actually he did, or something very close to it.
Yeah, the "something very close to it" is what I quoted. And I'll repeat: distinction matters.
> don't think you are going to get linear speedup by adding more people.
I didn't either say, nor imply, this. Of course communication and coordination is overhead. Let's quote Brooks from the same article some more: The maximum number of men depends upon the number of independent subtasks.
Which is why in modern times you have a bunch of theoretical and practical research around team topologies, DORA, Reverse Conway Manoeuvre, the push to microservices, etc, etc. You can boil all that down to "maximize team independence while making each team as productive as possible."
This is a wonderful tangent (and if this interests you, I heartily recommend the Team Topologies book), but can we just keep in mind the gp never actually said he was overhiring for a single project? Parent latched onto a wrong idea and ran with it.