Alternate Aesop Interpretation: The moral was meant to be "don't judge yourself by comparing yourself to others", but people have interpreted it as "don't discriminate against others based on their appearances", "different cultures have different standards of beauty", "if you feel like an outsider, you may be in the wrong group", an allegorical Gay Aesop, or "people can change over time".
Broken Aesop: Since the duckling is only accepted by the other swans, the aesop can come across as "stick with your own kind!"
Hollywood Homely: Baby swans are more or less identical to ducklings except for feather color. It's probably more a case of "beauty is in the eye of the beholder" since the other ducks still shun the titular ugly "duckling". Interestingly, in some versions where the old woman briefly takes him in, she comments on his ugliness, as well.
Misaimed Fandom: No, the Aesop is not 'stick with your own kind' or 'don't worry, you'll turn out to be beautiful'. The actual moral is about realising your own self worth and not judging yourself by the standards that others set for you. The 'duckling' believed himself to be ugly because he was comparing himself to how the other ducks looked, and they themselves bullied him because he was different from them.
Rainbow Lens: Like many of Andersen's stories, "The Ugly Duckling" is often interpreted as an allegory for his experiences as a bisexual man in the highly queerphobic world of 19th century Europe. The titular "duckling" is immediately singled out as different for his appearance and is bullied by his siblings, motivating him to run away before realizing as an adult that he was actually a swan all along, and that he only saw himself as ugly because all he could compare himself to were ducks, ultimately finding happiness with other swans. This arc is noted as having strong parallels with queer people's experiences with anti-LGBT+ bullying, internalized queerphobia, and forming a Family of Choice with other queer folks.
Tear Jerker: The fact that the titular duckling becomes so miserable that he throws himself at a flock of swans and asks them to kill him. Granted, the happy ending is still there, but damn...
Values Resonance: No matter the era, bullying, abusive parenting and discrimination for things completely outside your control have enshrined this story and its relevance, as opposed to some of Andersen's many, many less temporally enduring stories. That said, most adaptations tend to downplay the Sweet and Sour Grapes nature of the ending.
The Woobie: The title character. Seriously, who didn't want to hug the poor little guy?
Fridge Logic: Almost immediately after the "Winds of Winter" song, Augustus is kidnapped by some Savage Wolves, which are anthropomorphic and can speak, but do not sing. In a movie about talking animals, it was kind of a strange creative decision to give a singing part to the wind over these characters. They didn't even need to personify the wind in the first place.
One-Scene Wonder: The Winds of Winter and Frost only appear for one song number, yet they are some of the most popular characters in the film due to their smooth, menacing voices and awesome Villain Song.
Tearjerker: This film, which gives the titular character a bigger plot than the original story, has quite a few sad moments. One that stands out is when Augustus runs away from home while singing a rather depressing song.
The Woobie: While the duckling was already a Woobie in the original tale, this version expands on his tragic backstory, making him even more sympathetic.
