Depends. The cheap houses, yeah, there’s as fair bit of noise, but you can’t hear everything. From downstairs, you can hear when someone walks across the room above you, but not when they’re walking in other upstairs rooms. And from rooms on the same level, you can hear if someone is talking loudly in the room next door, but not enough to make out what they’re saying unless they’re yelling.

Well-built houses or buildings made for occupancy by multiple families usually have better sound insulation between the rooms/floors/units, so it’s not always an issue.

Edit: the plus side to that is I know all the noises my house makes at night, so as a light sleeper, I know when something is wrong in the middle of the night, and I only need one decent sound system for the whole house, which is great for listening to records while doing housework.