You try to speed up work by parallelizing, either by adding more machines or more humans. Seems pretty similar.
One is basically 1 + 1 = 2 and the other is a warning of a non obvious situation that comes from lots of experience and effort.
One is is good information from lots of experience, one is "the parts that don't use more cpus don't speed up with more cpus".
Unhelpful nonsense about running software vs battle won experience about making software.