George Harrison's frustration with the Beatles is very easy to understand when you learn they rejected "All Things Must Pass" during the Let It Be sessions. The band did run through it a few times, but ultimately the brilliant song was shelved. (Thankfully, extensive bootlegs from these sessions survive.) Harrison's songwriting abilities grew exponentially during his time with the Beatles, but John Lennon and Paul McCartney just didn't recognize this.
The public first heard the song on a 1970 Billy Preston album, and later that year, Harrison released a new recording of the tune on his triple LP All Things Must Pass. He never released it as a single, but it's become one of his most beloved songs. Let It Be would have been a better album if John and Paul had taken the time to appreciate the song.