But I think for many (most?) businesses, one nine is just fine. That's perfectly doable by one person, even if you want, say, >=96% uptime, which allows for 350 hours of downtime per year. Even two nines allows for ~88 hours of downtime per year, and one person could manage that without much trouble.
Most businesses aren't global. Downtime outside regular business hours for your timezone (and perhaps one or two zones to the west and east of you) is usually not much of a problem, especially if you're running a small B2B service.
For a small business that runs on 1-3 servers (probably very common!), keeping a hot spare for each server (or perhaps a single server that runs all services in a lower-supported-traffic mode) can be a simple way to keep your uptime high without having to spend too much time or money. And people don't have to completely opt out of the cloud; there are affordable options for e.g. managed RDBMS hosting that can make maintenance and incident response significantly easier and might be a good choice, depending on your needs.
(Source: I'm building a small one-person business that is going to work this way, and I've been doing my research and gaming it out.)
