I hear what you're saying but ... have you tried it? Seems like a simple enough exercise. Heck, maybe I'll try it.
Maybe it's because my outlook is generally one of being grateful, so I may have already received the benefits without this exercise.
In any case, I'd be wary of any claims like this unless someone tries it for at least 6 months. I expect initially one will get benefits but after N months it fizzles away.