It's never explained why Si-hoon is in such massive debt, despite having a promising career as a dentist. It's possibly due to either gambling or bad investments; as Gi-seok's office blacklisted him from receiving any loans.
Two of the songs from the show's soundtrack chime in at least twice per episode. To some degree, the songs give away the emotional state of the two main characters Ji-ho and Jeong-in. The song "No direction" plays whenever the two are thinking about one another or are within close proximity, but are prevented from meeting up for some reason. The song "Spring Rain" plays when the two are thinking about each other but do eventually meet up in person.