It's interesting that mnmom and Stage Right both mention thoughts about possible injuries first of all. The possibility of injury -- with the consequent need for time off, rehab, and slow regaining of form -- is a fact of life in all companies. Yet ballet dancing demands a look of insouciance -- something that is the opposite of looking as if you are careful.
5 senior dancers have been out with injuries this season in the company i follow most closely. A couple of these are noted for going all-for-broke in everything they do on stage. It must be extraordinarily difficult to keep in balance the natural wish to avoid injury and the personal artistic impulse to give everything you have.
Another thing: dancing in a company is a collegial experience. Dancers have to collaborate. What's more, they have to look as though they enjoy and even adore working with one another. Yet each dancer is in a sense competing with every other dancer -- for casting opportunities, publicity opportunities, and for one's job itself. Budget cut-backs, the emergence of newer, younger dancers, etc., are part of this. I guess all corporate jobs have these particular tension too, but it must be especially difficult in a world in which you are so often being scrutinized by the public.