Not 15 minutes into the movie, Ariel sings a deeply personal song about her fascination with the surface world and her Hoarders episode-worthy collection of random human junk. The tune might sound like your typical musical exposition, but it actually gives us much-needed insight into the mind of a rebellious teenager who seems to view dry land as a romanticized utopia, with lyrics such as: "Bet'cha on land they understand. Bet they don't reprimand their daughters."
Walt Disney Pictures
"Bet they understand that YOU'RE RUINING MY LIFE, DAD! GAWD!"
So when Ariel later saves Prince Eric and instantly falls in love with him, we understand what's going through her head, because to her, Eric is just the nearest available symbol of her lifelong obsession. (Also: literally the only guy she knows who has a penis.) Even when Ariel finally decides to sell her voice to Ursula, it's only after her father destroys her collection, which means that without "Part of Your World," the plot of The Little Mermaid simply makes no sense.
How We Almost Lost It:
Jeffrey Katzenberg, then chairman of Walt Disney Studios, didn't want the song to be a part of the movie's world because he thought kids would find it boring. He arrived at that conclusion after a kid in the test audience spilled his popcorn during the scene, which to Katzenberg meant that the sequence was so mind-numbingly dull, it actually caused the child's higher motor functions to commit suicide.