The large apartment building issue is a big one. I lived in a building (10 stories, 70 units plus commercial space on floors 1-3) for ~10 years. The first several years were great, not a single pest of any sort. And then the roaches (German cockroaches) started to show up.

The problem was that once they got into the building they were impossible to eradicate everywhere as no one, including the owners, were willing to bite the bullet and treat it as a whole-building problem. So instead you'd get little pockets of treatment and a never ending cycle was created.

Years later in our house we found and killed a single German cockroach. And of course, living in a city, if you find one that means there are many more. We were terrified. But after a single treatment by a pest control company we haven't seen any other activity for several years. Still have no idea if somehow we *did* only have that single one or what. But I'm not complaining.