"Picasso & Matisse. Manet & Degas. Pollack & de Kooning. Lucian Freud & Francis Bacon. This is the story of four pairs of artists -- each linked by friendship and a spirit of competitiveness. Taken together, they form an impressive lineage stretching across more than 150 years. But in each case, these relationships had a flashpoint, a damaging psychological event that seemed to mark both an end and a new beginning, a break that led onto new creative...