TLDR; The only thing that we as humans can do is project our beliefs upon the world, and consider them reality. This becomes a problem for the world if those views are ill-formed.
If John Citizen, a newbie internet marketer, tries to rank a site with 100k blog comments bought on Fiverr, and fails to rank top 3 most instantly, he'll start to believe that SEO 'doesn't work'. By the time he does one or two additional silly things, he'll be absolutely convinced that SEO doesn't work. That wouldn't be a problem if he kept that view to himself - the problem starts when he accrues a few hundred posts on a forum (and therefore, quasi-credibility) and starts replying to other unsuspecting newbies with 'the facts' that SEO doesn't work, OR that PBN's don't work, OR whatever poorly executed half-assed failure he ran in the days before arriving at that conclusion 'doesn't work'.