[jmull]

The advice here is contradictory. It suggests you should build and own things your business depends on, wherever possible, but also that you should buy things that aren't a core value of your core business.

There would very typically be a large overlap here.

Probably very few companies should build and run their own CDN and internet scale firewall, for example. Doesn't have to be cloudflare, but there aren't any providers that will have zero outages (a homegrown one is likely to be orders of magnitude worse and more expensive).