As with all jazz standards, this song applies to the most basic of emotions. In this particular song the emotion portrayed is the longing for someone in their absence. The song goes about to re-iterate the emotion by calling upon objects and everyday occurrences giving instance to the fact that such things become more mundane without the person there. For instance, a "tinkling piano" offers a raindrop type of visage which would tie directly into rain falling to correlation with tears of sadness or a dreary day.
