What is the theme in The Little Prince by Antoine de Saint-Exupery?

What is truly important cannot be seen is another theme in the story. This theme is introduced early on when the pilot tells of drawing the boa constrictor from the outside. None of the adults can see it for what it is, because although the boa constrictor's body is bulging, the boy has not taken the pains to draw the elephant inside. It is the imagination, which requires a connection to the heart, that allows the little prince to see on first glance, what the adults are unable to see.