George Martin on the Revolver Album

"I'm not sure they ever stopped being a good rock-and-roll band. I think once they'd got their first success under their belts that seemed to spur them on to greater songwriting efforts. John and Paul, having found out that it was comparatively easy to make a hit with 'Please Please Me' and then 'From Me to You,' said, 'Great, we know how to do it.' It then became a production line, and their ingenuity was actually spurred on by their success at that stage. They were always thinking of fresh ideas and new things, and each song that came out seemed to be a good one. I don't think they really started developing their best songwriting skills, in a really strange way, until Revolver. I think that was the beginning of the breakthrough, and certainly 'Tomorrow Never Knows,' on the end of Revolver, was the beginning of the so-called psychedelic bit, which was the forerunner of Sgt. Pepper."