Trying to explain Brooks' Law to a project manager is like showing them these two chickens. On the left: a chicken burnt to a crisp after 1 hour at 900°F. On the right: a perfectly roasted chicken after 3 hours at 300°F.
The PM's brain short-circuits when you tell them that nine women can't make a baby in one month, and throwing more developers at a late project just creates more merge conflicts and onboarding overhead. But they'll still ask if we can "just parallelize the work" while ignoring the codebase slowly turning into charcoal.