The theory sounds like it's about kindergarten kids mostly. Some people probably continue to desire something others do (isn't the whole fashion idea built on this?) in the older age as well.

I have not observed it myself, but again I have heard that is what social media is about.

At least from my childhood I remember I sometimes wanted what others have, but it was probably more because I has hands on on some interesting toy, and imagined my own use for that. Though I remember there were kids, who desperately wanted something I had... I do not think the theory is that universal.

I hope humanity is not as primitive as described in this article. It only takes starting to reflect on one's own thinking process and widen one's horizon beyond hedonism and selfishness.