Indeed, Thomas Jefferson probably did know what the real implications when he said "...the right to pursue happiness.". In fact if you really look more deeply at this statement it has the opposite effect. The more you chase after happiness, the more it runs away from you. Its like jumping in your car and trying to reach to the horizon. There will never be any progress made, the horizon will keep moving away from you.
This implies that by chasing after happiness, one will only become frustrated and find oneself in a misery.
So...Jefferson's statement essentially means we have the right to remain miserable!