"Let Him Run Wild" was one of the first songs that Brian Wilson wrote while under the influence of marijuana. According to Wilson, the song is "about a girl who was dating a guy who didn’t stay close to her. The guy singing wants the girl to let her boyfriend run around and eventually leave her so he can come in and get her. He wants a bad thing to happen so that it’ll turn into a good thing."
Biographer Peter Ames Carlin suggested that the song was inspired by the extramarital affairs of Brian's father Murry.
A soulful ballad, the song is said to have been inspired by Burt Bacharach while also foreshadowing the relatively complex music dynamics of Pet Sounds several months later. Author Jim Fusilli explained, "it's a gorgeous track, albeit a bit busy at the chorus when compared to what's ahead, with major seventh chords that ring beautifully. The song's subtle horn charts, prominent tremolo bass, the vibraphone, and the sweet, pensive section after the chorus portend the sounds of a forthcoming classic." MOJO wrote: "With key and tempo changes bolder and weirder than anything before, this was Brian's signpost to the psychedelic country up ahead."
Among the band members, Carl and Dennis Wilson reflected on "Let Him Run Wild" as the point where they began to take notice of their eldest brother's true talents as a writer and arranger. Al Jardine expressed a similar sentiment, stating, "In terms of the musical direction Brian was going, I always thought that 'Let Him Run Wild' was the turning point, the beginning of that phase when things began to get more complicated." From: https://en.wikipedia.org/wiki/Let_Him_Run_Wild
