It's simple really. If you increase the value of 100 by 10% and then decrease the resultant by 10%, you get an overall reduction in value (even if you do it the other way around) ;)
I have read that in studies, people require a gain of $2 to make up for the loss of $1, and it would have illustrated the point beautifully, but I couldn't find a citation. Alas!
I first read about it in Dan Ariely's "Predictably Irrational".
I enjoyed the post but I'm struggling to figure out exactly the point it was trying to make?
I found the result worthwhile as a counterweight to negative thinking. I showed the draft to a close friend and he had a similar reaction which was "so what?" I fleshed out the conclusion a bit more, but you're right that it still doesn't have a strong takeaway. I might just be too wrapped up in my interest in empirical studies of human happiness to write a really useful blog article on the topic, but I've got to keep trying! :)