Almost every evening [in their common early-Cubist years, in Paris], either I went to Braque's studio or Braque came to mine. Each of us had to see what the other had done during the day. We criticized each other's paintings. A canvas wasn't finished unless both of us felt it was.

Picasso to Françoise Gilot, December 1908. As quoted in Futurism, ed. Didier Ottinger; Centre Pompidou / 5 Continents Editions, Milan, 2008, p. 311