Another consideration (sorry to add to the rabbit hole) is HVAC ducts and vents.
Sound is like water, if there's a hole somewhere, it'll find it.
That being said, each cumulative layer of sound diffusion, mass and air gaps all work together to mitigate sound propagation. You want the highest cumulative STC (Sound Transmission Control) rating. So for your example, ideally you'd want and STC rating of 50 and higher.
https://en.wikipedia.org/wiki/Sound_transmission_class
Stupidity is a disease we all have, it's like a form of brain herpes. Outbreaks will occasionally occur.