TORONTO, March 1 -- It's often said that happiness is the result of hard work on one's self and one's life plans. One has to fight to achieve this state, sometimes even travel the world to find it. But what if, paradoxically, trying to be happier actually made us sadder?

At least, that is the finding of a study conducted by researchers at the University of Toronto Scarborough in Canada and published in the journal Applied Psychology: Health and Well-Being. The study reveals the existence of a "happiness paradox": the more we try to be happy, the more mentally exhausted we become, to the point of reducing our ability to make choices that are truly beneficial to our well-being.

For over a decade, scientists have been interested in examini...