"one man's trash is another man's treasure" .this is such an important but underrated  statement in do you like brahms. joon-young is so extremely talented in piano but piano was never his " life" his entire reason to live etc. the way it is for most musicians/artists. he "worked" for jungkyung and her grandma, because mrs nah provided his family money. 

where as song-ah was in love with music, her passion was piano but lacked talent and neither did she have the time to make up for lack of talent.

if joon-young had song-ah's love for music. and song-ah had joon-young in born talent, entire situations would have been so different