Yamamoto advised Kurosawa that a good director needed to master screenwriting. Kurosawa soon realized that the potential earnings from his scripts were much higher than what he was paid as an assistant director. He later wrote or co-wrote all his films, and frequently penned screenplays for other directors such as Satsuo Yamamoto's film, "A Triumph of Wings" ("Tsubasa no gaika", 1942). This outside scriptwriting would serve Kurosawa as a lucrative sideline lasting well into the 1960s, long after he became famous.