This song is aboutl an artist losing their passion. It's based on Martha Graham quote (which I'll paraphrase as I don't remember it word for word). An artist dies twice and the first death is the hardest. Hope that helps.
Martha Graham's Quote "A dancer dies twice - once when they stop dancing, and this first death is the more painful." Basically, Black Swan is about what any person who lives for making art faces: losing the passion for creating. Much like a dancer feels purposeless when they can no longer express themselves through dance, BTS contends that the day that music no longer fills them with the same passionate fire as before, or even if there came a day when they stopped creating music - what they feel is their life's purpose - it would feel like death. Leader RM sings, "If this can no longer resonate / No longer make my heart vibrate / Then this may be how I die my first death."
BTS frequently fades to black right before the final scene...so be careful about stopping the video too soon because you know how we ARMY can be about those things...lol.
Along with everyone's else comments with it being about losing passion for the arts- they shot their mv in a theatre on a stage where performers dance etc. Beautiful location! And their dance moves mimic the black swan. Really gorgeous!