What he says aligns with something I wrote about over a decade ago. I call it the Theorem of Four SEO Influences. There are four reasons for why your search engine rankings change: 1) You do something with your site 2) Someone else does something with their site 3) The search engines do something with their data 4) People search for something different Everything that happens in a search system is influenced by these four input channels or vectors. A change in any of these influences can alter the search results, and all four change constantly.