In early June 1966, The Rolling Stones ruled the airwaves on both sides of the Atlantic with “Paint It Black.” That track, which hit No. 1 on the Billboard and UK charts, featured a driving rhythm and a sitar part played by Brian Jones.
But The Beatles weren’t looking to their purported rivals for inspiration as they recorded Revolver in April-June ’66. A year earlier, George Harrison wrote a song that reflected the influence of The Byrds (“If I Needed Someone”) for Rubber Soul. (George played sitar on that ’65 album as well.)
Meanwhile, Paul McCartney was hitting a peak during the Revolver sessions with ballads like “For No One” and “Here, There and Everywhere.” And on “Good Day Sunshine, the album’s bounciest song, Paul looked to another American band for inspiration.
On that short and sweet track, Paul said he had The Lovin’ Spoonful in mind. But Paul didn’t play the barroom-style piano on “Good Day Sunshine.” Those honors went to the best pianist in the studio that day.
Source: cheatsheet.com