Music researchers analyzed over 700 top Billboard songs (which included examining over 80,000 chords) and they determined that the "Ob-La-Di-Ob-La-Da" is the most appealing song ever written. How in the world, you might ask, did they choose that (some would say annoying) song?! Let's find out how two key ingredients - surprise and uncertainty - combine to create songs that you really like to hear over and over.