Even the greatest anime feature moments that viewers find objectively terrible. In fact, some of these moments are so bad that they make you want to rage-quit the whole series. If you do keep watching, you can't stop thinking about that moment, and it colors your perception of the series as a whole.
Some anime moments that made you want to stop watching involve character deaths that change the story, but not for the better. A lot of Death Note fans tuned into the show because of how much they loved L - so they weren't willing to stick around for what happened after he died. Plenty of anime deaths are sad, but not all of them completely shift a storyline the way L's does on Death Note.
Other times, it's a moment where a character does something terrible that's either out of character or makes you realize how much you don't like them or care about their story - it's hard to love Haru Yoshida or get invested in his relationship with Shizuku after he threatens to assault her. Maybe it's a moment where the writing is so bad that you can't ever look at the series the same way again - did the creators of Sword Art Online even know why Kayaba killed all those people? If they did, it's sure not clear from his cop-out explanation at the end of the series.
Let's cringe together and see if we can get through this.
Ash Ketchum doesn't need to win every Pokémon battle to be worthy of attention, but he should probably win at least some of the time. His losses always feel at least a little disappointing, but his failure to defeat Alain in Pokémon XYZ truly stings. Why? Because Ash had type advantage! He pitted his Greninja (a water type) against Alain's Mega Charizard (a fire/dragon combo).
There's no connection between dragon and water, but water has a clear and obvious advantage against fire. Type advantage doesn't mean an automatic win, but by this point, Ash has had so much experience that the loss seemed less like a natural outcome and more like a reason to lose faith in Ash as a character.
When Goku transforms into a child thanks to someone else's careless wish, producers were likely attempting to recapture the charm of the original Dragon Ball. But if people want that, they have a better option - go re-watch Dragon Ball.
Goku losing every ounce of character development he's received over the course of the series is less charming and more straight up irritating, and it made a lot of people lose confidence in what was coming next for GT.
To some Death Note fans, the series ceases to exist beyond the first season. That's because they stopped watching after L's death. It's not that important characters should never die, or that L's death was handled especially poorly - it's that he was one of the best things about the show, and nothing that follows afterward truly made up for the hole he left in the show.
While some viewers find what happens afterward worth it, and find second season characters like Near, Mello, and Mikami compelling, others just don't see the point. This was especially true when the series first debuted, and his death provided a total surprise to dedicated fans.
Instead of a single moment, this one actually consists of a whole season. The first season of The Melancholy of Haruhi Suzumiya makes for awesome viewing. It opened up new possibilities for how the supernatural, slice of life, and parody genres could combine, and you couldn't go to an anime convention without seeing at least three groups of people doing the Haruhi dance in the hallway. But the second season featured an arc that viewers found so infuriating, the notorious Endless Eight, that many just didn't want to watch anymore.
The Endless Eight was an arc in which the characters find themselves reliving the same experiences over and over again, Groundhog Day-style. This could be okay - except they drag it out for eight full episodes which are virtually identical except for a few minor changes. That's enough to try the patience of even the most dedicated Haruhi fan.