But even though Mr. Pitt’s coolness is a perfectly defensible approach to this character, his elusiveness, from one film to the next, is starting to look more defensive than daring. His recent performances have been devoted mainly to the study of his own magnetism, a quality he earnestly explores in“The Assassination of Jesse James by the Coward Robert Ford” and playfully subverts in “Burn After Reading.” It goes without saying that Mr. Pitt has charisma to burn, and he is a capable and inventive actor, but he will only be a great one if he risks breaking himself open on screen as he did, briefly, in “Babel.”