I'd add to his argument, that the problem with software and uptime is that every time we add a layer of abstraction or library, the five 9s factor may apply.

    Math.pow(.99999, 1) - One dependency.
    Math.pow(.99999, 2) - Two dependencies.
    ...
    Math.pow(.99999, N) - N dependencies.

And that assumes everyone is aiming for 99.999% uptime. Which isn't true.

There's other factors, but that's the one I'd point out.