Unhappiness is a very personal thing, but if any generalization can be drawn at all, it is that most people are usually convinced that they are the most unhappy / miserable/ unfortunate / troubled / sorrowful / despondent ( delete where appriopriate ) person on earth. I don't think anyone will have any problems understanding that, we have all been, at one point or other, been convinced of its truth, generally because one's own problems are immediately identifiable, whereas trying to walk in someone else's shoes may be a tad too troublesome. Plus, everyone fancies being chronically misunderstood.

Point is, of course that we always convince ourselves that if we just do a little bit better, or if we get that damn promotion which is just without our reach, our happiness will be complete and we will finally be able to sit down and enjoy the feast of life. That does not happen very often, just as a student who fails his exams will aim to pass, while someone who passes it comfortably will aim to excel, and those who excel will hanker for the top spot, because we will forever covet what we do not have.

And even if we do get what we want, we usually lose our appetite for the feast in the process.