The problem with that formula is whatever it is you have to consider that humans are still building houses and building them wrong/inefficiently. PVC pipes, iron, copper pipes....you can't use certain products with those. So you're always going to have that person, group of people that puts/pours that shyt in there sink, toilet, floor drain and fukks there shyt up.
shyt in my house I have a breaker that's 20amps and my shyt is wired for 15.
There's some shyt computers or ai just can't fukk with and humans are making it more difficult for other humans because we're protecting these industries. There's a lot of certifications, licenses, apprenticeships one has to get to become a plumber or electrician and for good reason but they're growing increasing more difficult. Deciding at 40 you want to become an electrician because you've always liked it and even have skills is pretty much dead.