Co-written by Eldredge and Jordan Reynolds, this song is an introspective look at the singer's journey with love. "'Castaway' is one of the most poetic songs I've written," Eldredge said. "It's the story of how you go through something for so long on your own and think that you need to continue to chase it, but you get so far away that you're deserted. You're a castaway. You figure out the thing you needed the whole time was love. I think more than this being about some certain person, this song is my story, my relationship, my letter to love."
The song's music video shows the inner struggle Eldredge sings about as we see him walking alone past a woman and onto the stage at an empty Ryman Auditorium in Nashville. By the end, the woman has wandered into the Ryman and sat down to listen to Eldredge, unnoticed by the singer.
When "Nothin' On You" reached #1 on the Hot 100, B.o.B became the first American act whose name is a palindrome to top the chart. The other two who did so prior to the Atlanta rapper were both Scandinavian groups - ABBA and A-Ha.