"It has been observed in all ages that the advantages of natu..." — Samuel Johnson quote meaning

It has been observed in all ages that the advantages of nature or of fortune have contributed very little to the promotion of happiness; and that those whom the splendour of their rank, or the extent of their capacity, have placed upon the summits of human life, have not often given any just occasion to envy in those who look up to them from a lower station; whether it be that apparent superiority incites great designs, and great designs are naturally liable to fatal miscarriages; or that the general lot of mankind is misery, and the misfortunes of those whose eminence drew upon them an universal attention, have been more carefully recorded, because they were more generally observed, and have in reality only been more conspicuous than others, not more frequent, or more severe.