Only a tiny fraction of businesses can't afford downtime. A lot of businesses claim they can't afford downtime, yet don't insure against it, and don't invest enough in high availability to be able to reasonably claim they've put in a decent effort to avoid it.

In most cases I've seen of businesses that claim they "can't afford downtime", they quickly balk if you present them with estimates of what it'd cost to even bring them to four or five nines of availability.

> A system that can't tolerate downtime probably has an on-call rotation and these triggers ought to be reasonably fast.

A lot of such systems can still run up large enough costs quickly enough that it's a major problem.

> If you can't react or can't afford to react, you probably can afford some downtime / data loss.

I'd say it is the opposite: Those who can afford to react are generally those with deep enough pockets to be able to weather an unexpected large bill best. Those who can't afford to react are often those in the worst position to handle both the unexpected bill and the downtime / data loss. But of the two, the potential magnitude of the loss caused by downtime is often far better bounded than the potential loss from a crazily high bill.