For a pure tech company this might be good advice, but lots of startups require domain expertise from very early on even if that means partnering with a nontechnical founder. E.g., my background is in insurance, I've seen lots of insurtech startups founded by engineers without insurance backgrounds, and in my experience they don't tend to be successful.

In an ideal world you'd want every founder to have background in the relevant industry and strong business sense and the ability to build the product, but being strict about all of those criteria would result in a lot of false negatives.