Here is an abbreviated timeline of the how the video above came to be.
In 1988, Crystal Light—the fluorescent beverage of the fluorescent '80s—hosted what is possibly, in retrospect, the most '80s event imaginable: a national aerobics championship.
In 1989, Taylor Swift was born.
In 2008, the scholar Lawrence Lessing released his book Remix: Making Art and Commerce Thrive in the Hybrid Economy. The book argues, among other things, that the Internet—and the tools it has provided for easy editing and sharing of cultural products—have fundamentally transformed the way we approach authorship and ownership and creativity.
In October of 2014, Taylor Swift released the album 1989. Which is heavily influenced by the music of the 1980s.
In November of 2014, a YouTube user named Thomas Jung found footage of the 1988 Crystal Light National Aerobic Championship. He realized that the '80s-tastic choreography of the competition's opening ceremony matches the rhythms of Swift's '80s-influenced song "Shake It Off."
In November of 2014, Jung created a video that overlays "Shake It Off" onto the footage from the aerobics routine.
In November of 2014, Jung posted that remixed video to YouTube. News of it spread.
In November of 2014, Taylor expressed her appreciation for Jung's application of her song:
A sneak peak at the official "Shake It Off" choreography for the 1989 World Tour: http://t.co/go43vmoNMO— Taylor Swift (@taylorswift13) November 7, 2014
In November of 2014, in other words, because of some combination of Taylor Swift, Thomas Jung, YouTube, Google, the 1988 Crystal Light National Aerobic Championship, a butterfly flapping its wings, and the fact that players gonna play (play, play, play, play) ... delight ensued.
Hat tip @eleanorbarkhorn