Ah, I see! I agree. That paragraph is an excerpt from the website (as I was on my phone and didn't feel like summarizing the full theory).

On a macro level i.e. comparing people with vastly different circumstances/experiences/variables it does seem questionable, but on an individual level the change can be quite profound, going from a self-defeating to a more open/growth oriented mindset.

Also reminds me of one of my favorite quotes, by Henry Ford:

“Whether you think you can, or you think you can't--you're right.”