Ballet dancers are a self-chosen elite. To survive and surmount years of disciplinary preparation and seasons of even more arduous performance requires rigid determination and almost mindless self-abnegation. One other factor is difficult to predetermine: without a certain admixture of hysteria - sometimes masking as self-obsession, sometimes even counterfeiting incipient madness - performers, at once acrobats, artists, and animals, make little public impression.