Not for everyone, but it is true for the average.

It is especially reinforced nowadays with Social Media and with people who have less sources of self-worth.

The less you have to hold onto the more you invest in what you have, and the harder you fight to keep it; almost like an animal driven into a corner.

It will always depend on the individual, but a good kind of question to ask would be this:

"If you had more money/fame/popularity/status, or if you looked better/healthier/more muscular/prettier, or if you had more achievements/awards/certificates than person XYZ, would you be happier than you are now?"

If the answer to that is "yes" then it means that person associates that thing with happiness, and likely success.