Sinatra asks " Where Is The One ?"  I believe that most single people have cast thoughts about that certain someone who might be one's desired life partner. Sinatra, himself, had imagined such thoughts, found partners who were not compatible before ending up with Barbara Marx. Alec Wilder, was also a song scholar who  wrote the song. The longing in Sinatra's voice and the pleading in the lyrics combine to create a highly emotional listening experience.

https://youtu.be/KpsT6uHVgoI