"Lost" is an R&B and pop song set in common time at a straight-up pop tempo of 123 beats per minute. The song is in a G minor, with a chord progression of Gm−B♭maj7−E♭−B♭maj7 followed throughout, and Ocean's vocal spans from C4 to G5. According to The Quietus, "A bouncy indie-rock rhythm and chicken-scratch guitar propels a buoyant Frank, as he takes to the road in the hope of getting well and truly lost in sunny California. Flowing atop a narcotic bass melody and a trio of harmonising vocalists, the choruses eventually pan back for a coda of whistling synths and ELO-esque keys." The lyrical content of "Lost" describes the protagonist's relationship with a cocaine-cooking girlfriend. The song contains samples of the film Fear and Loathing in Las Vegas (1998).
"Lost" has received high praise and acclaim among critics, praising Ocean's idiosyncratic style and pop sensibilities as well as Malay, the album's prominent producer. It is often referred to as a highlight on his debut studio albumChannel Orange and is his most straightforward "pop" song.
"Lost" achieved its greatest level of success in New Zealand. The song debuted on the New Zealand Singles Chart at number 32, peaking at number 5 three weeks later and becoming Ocean's first top-ten single. The song was eventually certified gold and subsequently platinum by the Recording Industry Association of New Zealand (RIANZ) in its fifth and ninth week on the chart, respectively.