I suppose more concretely "doing something related to what you are writing about". On principle I have nothing against pure philosophers, who integrate old theories and formulate new ones. However, in my experience, writings like that of Marcus Aurelius are more compelling, who was a success in his own right before ever writing anything. Most modern "business" authors don't have any business (other than selling books to people). Taleb is just warning people to not take advise from authors who don't actually have "skin in the game".