This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Winnie-the-Pooh
The ending of The House at Pooh Corner: Christopher Robin is going away. It's implied he's going to boarding school, which means he won't see his friends again. The characters don't know the specifics, but they band together and write him a goodbye note. As they host a farewell party, Eeyore realizes that the boy wants to be alone with Pooh, and tells the others to leave. Christopher Robin then takes Pooh to 'An Enchanted Place at the Top of the Forest'. They talk together about doing nothing. Christoper Robin mentions that 'they don't let you do nothing. Not for long, anyway.' He tells Pooh of things he'll learn at school—about countries, Kings and Factors, eventually making him his best, most faithful Knight. Then the ending.
"Pooh, promise you won't forget about me, ever. Not even when I'm a hundred." Pooh thought for a little. "How old shall I be then?" "Ninety-nine." Pooh nodded. "I promise," he said.
Still with his eyes on the world, Christopher Robin put out a hand and felt for Pooh's Paw. "Pooh," said Christopher Robin earnestly, "if I — if I'm not quite —" he stopped and tried again — "Pooh, whatever happens, you will understand, won't you?"
"Understand what?" "Oh, nothing." He laughed and jumped to his feet. "Come on!" "Where?" said Pooh. "Anywhere," said Christopher Robin.
So they went off together. But wherever they go, and whatever happens to them on the way, in that enchanted place on the top of the Forest a little boy and his Bear will always be playing.
Surprisingly, the ending was copied almost word for word in the ends of both The Many Adventures of Winnie The Pooh and Pooh's Grand Adventure. Slightly toned down yes, but the implications are still the same-and it's just as sad.
Rabbit's Bad Future if he succeeds in making the first day of Spring officially "Spring Cleaning Day". His friends will find him so overbearing and controlling, that they will all move away and leave him alone.
The scene is made even more painful to watch when at first he thought everyone leaving due to being an overbearing authoritarian was some kind of sick joke, only to be proven otherwise and become more desperate as the scene goes on. We even notice that the Hundred Acre Wood is becoming more barren as the scene moves on. What drives it home harder is that when he gets to Roo's and Kanga's place, he finds absolutely no one there... and in that moment of pure regret, he utters "What have I done? Where are all of my friends?" in this sad voice.
The backstory explaining why he's come to hate Easter. After one especially overbearing year as the Easter Bunny, Tigger snuck off with the eggs and the gang went to do hunt them without him. This wasn't what broke Rabbit however. It was how much Roo loved Tigger playing Easter Bunny. He felt rejected since he wanted to make something nice for Roo, but couldn't compete with his Big Brother Worship of Tigger.
Tigger did try to apologize for making Rabbit feel like this, but Rabbit wouldn't hear of it and so, Tigger went away dejectedly saying that they'd never celebrate Easter in the Hundred Acre Wood again.
Pooh's Heffalump Movie
Lumpy is lost in the forest and trying to get back to his "mummy," but ends up caught in the heffalump trap set by Pooh and the others.
Lumpy: (to Roo, sobbing) You said they wouldn't be scary.
Roo: Oh, Lumpy. I'm so sorry. This is all my fault.
Lumpy: I want my mummy.
Poor Eeyore being Demoted to Extra and being forgotten about by the others until the end of the film.
Winnie the Pooh (2011)
The trailers, with "Somewhere Only We Know" playing over them. Really hits home for people who have grown up with these stories and are adults now.
The look on Pooh's face when his friends gave the jar of honey to the red balloon.
And the resulting conversation with Eeyore.
Pooh: Ever have one of those days where you just can't win?
Eeyore: I know exactly how you feel.
Seeing that almost half the voice actors who worked on previous Pooh productions wouldn't return for this film, including Peter Cullen (Eeyore), Ken Sansom (Rabbit), and Andre Stojka (Owl), the former two in fact were reportedly disappointed they weren't called in for their roles. Especially since Sansom died the following year. Cullen however, was brought back for the Doc McStuffins crossover.
The ending of The Many Adventures of Winnie the Pooh is this mixed with a heavy dose of Fridge Horror if one considers the Christopher Robin in the stories to be the Christopher Robin (the son of A. A. Milne who inspired the original books). At the end of the film, Christopher Robin has to tell Pooh that he is about to start school and won't be able to play with him as often anymore. In real life, Christopher was bullied at school for inspiring the stories, leading to some level of resentment of his father for (in his eyes) exploiting his playtime adventures and the public attention it netted him for life, until finally donating the stuffed toys he played with as a child to the editor of his first autobiography (though now they are at the New York Public Library). For all the fun he had with Pooh and pals, and the joy his fathers stories have brought to children around the world, the suffering he was put through later in life is made all the more tragic by just how unnecessary it was.