Brian Wilson and Glen Campbell, who briefly replaced Wilson in the Beach Boys between 1964 and 1965, had an unusual bond. Campbell was a session guitarist familiar with the band's sound and played on several songs. Wilson and Campbell collaborated on the song "Guess I'm Dumb," which was rejected as a Beach Boys song but shared it with Campbell. The next time they worked was after Campbell died, when Wilson added his vocals to Campbell's song "Strong," which addressed Campbell's concerns about his Alzheimer's diagnosis.