"The pot calling the kettle black" is a proverbial idiom that may be of Spanish origin of which English versions began to appear in the first half of the 17th century.
The idiom is glossed in the original sources as being used of a person who is guilty of the very thing of which they accuse another and is thus an example of psychological projection.
When I started re-enjoying Disney movies I was loath to try "The Black Cauldron" since it was never something that I enjoyed watching growing up. This was a risky move. And it demanded a little bit of thought to get it right.
I don't think it's a particularly good effort by Disney, it was different. Though I can look at it now and appreciate it for what it is. Back then Gurgi was the only good part of the movie and he still is.
The art direction is great in "The Black Cauldron" and I assume that this the reason it was one of my brother's favorite Disney films as a kid. Watching it now I see how dark it really was and why it did not appeal to me.
Audiences weren't necessarily prepped for a darker movie in the 1980's, the film had budget issues across the board, the plot tried to condense a lot of material. At the time it just didn't feel like a traditional Disney movie. It was darker and put off some families.
This was because Disney had purchased the rights to the whole series. It was named after the second book but also tried to cover the first and then veers in a different direction and the pacing occasionally struggled because of this. On top of that the characters come and go with little development, which makes them forgettable. The film's atmosphere feels oddly empty, as if there's no world or characters beyond what shows up on screen. Compare that to something like "Beauty and the Beast" which features a lively castle, rowdy bar, village, etc.
As for story it took a simplified direction with the material like many Disney stories and the story they did try to tell was visibly undermined by censorship. It's very poorly paced compared to better example of Disney animation for decades before and it is clear that it has been reworked from the editing. Another reason was because it was the last of the Disney "gag men" style of animated feature.
I admire that the movie is a bold attempt for Disney to use a darker style, rather than the usual stuffs they were producing, however, I just don't think that lives up to the better movies that came out before it. Still, I also feel that the darker-tone of the movie inspired some of the more mainstream fantasy movies of the 80s and against them it holds its own. Though it is not a great film as such "The Black Cauldron" is far from the worst Disney movie. And the hate that it receives is unjust.