Look, I don't want to trip over my own trope but, for me, the highest reward for a person's toil is not what they get for it, but what they become by it. Where have I heard that before? Wait, what were we talking about?
Apparently, according to D.G.R., gratitude has to be directed towards someone. Without this transfiguration of ones' gratitude, the experience is full of anguish and despair? Pain and suffering also comes to mind when describing the worst moment one can experience.