This string-laden track marks a more playful sound for the xx. DJ-producer Jamie Smith told Spin magazine regarding the origin of the tune: "We were in a lull trying to work on something else and not getting anywhere so we just started playing this and by the end of the night we had a song."
Singer-guitarist Romy Madley Croft added: "[The song] is quite a new thing for us. It's a bit of a different groove. Oliver [Sim] plays quite a fun bass line."
The song likens the highs and lows of a relationship to that of the tides. However, the pared-back lyrics are typical of Sim and Madley-Croft's impersonal material. "I don't want the details of our life to limit the imaginations of the people who listen to our music," said Sim to Spin. Romy and I have been thinking a lot about someone like Sade. Her music of course — it's so sensual — but more the fact that you don't know anything about her. That to me is the height of cool. Remaining mysterious like that. It's abnormal to know everything about anyone. Maybe in the last few years, there's been the expectation that we should know everything Katy Perry thinks and does, but in the span of human history, privacy is the norm. That's what people protect."
"Piano Man" was inspired by Billy Joel's time playing at a piano bar in Los Angeles. The "real estate novelist" was a guy who always talked about writing a book, but spent all his spare time in the bar.