You must remember this:
A kiss is just a kiss,
A sigh is just a sigh.
The fundamental things apply
As time goes by.

Herman Hupfeld (1894-1951) American songwriter

“As Time Goes By” (1931)
    (Source)

Hupfeld composed the music and lyrics for the song, which first appeared in the largely forgotten Broadway musical, Everybody's Welcome (1931). The song is more famous (and only remembered today) for its performance and use as a recurring theme in the film Casablanca (1942), where it was included over the objections of Max Steiner, who composed the rest of the music for the movie.