This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Documentary
The little girl in the documentary The Dark Side of Chocolate with the open wounds in her legs. Also, the little trafficked boy crying. It's sad that this goes on and so many don't know about it.
The Falling Man is a documentary that should be regarded not in terms of a single tearjerking moment, but how it manages to make the viewer break down so many times in an hour and a half. The first five minutes are a collection of news and radio fragments designed to hearken back to the confused mood that many people felt when they realized that New York had been attacked on September 11th. The descriptions of the final phone calls from people who were in the towers themselves. The description from a widower about how his wife was found on the pavement outside the wreckage because she jumped ("For those few brief moments, it must have felt like flying"), the unused photos from Richard Drew's set on "The Falling Man", how the media attempted to cover up the image so that others wouldn't be depressed by it, or the owner of Windows on the World trying to find the man's identity because he wanted to give some small measure of hope to a family. It's beautiful and tragic at the same time.
Nine Eleven: In the CBS documentary of the same date, one of two French filmmakers (who were covering the life of an NYC firehouse before the attack) is inside WTC1 with a number of firemen and police officers. During their evacuation of the mezzanine, a constant thumping noise can be heard in the background. The fire fighters realize that the noises are coming from jumpers who are hitting the mezzanine roof and the pavement outside. There's a shot of the platoon fire chief standing with his walkie up against his mouth, wide-eyed and struggling to hold his emotions in when he hears another crashing noise outside. Later on, the two brothers reunite in the firehouse and meet back with everyone who's left. There's complete confusion, and many of the firemen are explaining the casualties and missing friends in disbelief. One of the final images is a firefighter from the firehouse raising the American flag, just like any other night, but now with a very different meaning. Tears.
There was a 9/11 documentary made for The History Channel a few years ago, called 102 Minutes That Changed America, which was comprised of amateur and professional footage and audio taken that day, with no narration. The raw emotions of the multitudes of people in the footage — fear, hopelessness, disbelief, sadness — is enough to evoke all kinds of tear jerker reactions. There are obviously too many moments to list, but one of the most heartbreaking moments came from a small child who appears on camera in her apartment near the end, looking out her window to the spot where the towers once stood, and innocently remarking about it:
Little girl: It's not there anymore. The World Trade Center, right, daddy? It's not there anymore...
The above gets even sadder during the 15th anniversary airing in 2016, when the girl (now fully grown) and her father are interviewed for bonus footage. The girl remarks that 9/11 affected her more deeply than the documentary let on, and the father reveals that he and the mother (whose reactions could also be heard in the documentary) split up a few days after the attacks.
A amateur cameraman who takes refuge from the debris cloud in a restaurant catches footage of a firefighter making a call to his parents and telling them that he's alright.
The image of a group of firefighters bravely matching into one of the towers with their equipment on, just a short while before they collapse.
The shots of the firefighters who make it to Ground Zero after the collapses and see the wreckage, which looks like Hell on Earth. The firefighters simply stand and stare in disbelief, with one man having a Heroic B.S.O.D. and being unable to move.
A CNN documentary on cancer once interviewed several people who had either survived the disease or lost someone close because of it. At the end of the documentary, they asked all of them the same question: "If you made a movie about cancer, how would you end it?". Many talked of an ending of people triumphing over adversity, but the one that hits hardest was the simple, selfless response of an old widow who had lost her husband to cancer:
Widow: It would end with a man in a lab. And he would say "Eureka".
Link TV showed a documentary on a refugee from Iran returning to revisit his family that was called Relocating Mountains.
The documentary series 7 Up! followed a group of people from England from different social classes from the age of seven in 1964. The first one had someone asking Paul, a little boy in a children's home, if he wanted to go to university. He frowned and asked, "What does university mean?" Then there was Bruce, who was at boarding school and whose 'heart's desire' was to see his daddy...
A documentary on the French Revolution's Reign of Terror brought this into a straight "My God, What Have I Done?" moment. Madame Du Barry was being taken to the Guillotine, and the actress acted much like the historical documents say she did - constantly trying to escape and screaming, "You're hurting me! Why?!?". The narration mentions that her screams of terror could be heard all throughout the city, and how it took several men to restrain her.
Anvil! The Story of Anvil: Two lifelong friends of a metal band, Anvil, who once shared the same stage with acts like Slayer and got good reviews but just never made it. Decades after their promising start, the two middle aged men are still trying to get their big break. It's a sad to see those two are still struggling to make a living, but at the same time, it's moving to see that their friendship still remains strong.
Derailroaded is a 2005 documentary about Wild Man Fischer, a schizophrenic street musician who is still poor and homeless despite having made records with names like Frank Zappa, Barnes & Barnes, Rosemary Clooney and appearing on Rowan & Martin's "Laugh-In". The documentary shows how Fischer missed a lot of opportunities to break to the mainstream because his mental state is so unstable. He either physically attacked people who meant well or got stage fright. The documentary has no happy ending, unfortunately: Fischer died in 2011 as poor and insane as he always was. But the documentary brought him new media attention.
The Devil And Daniel Johnston is a 2005 documentary about bi-polar outsider musician Daniel Johnston. Johnston did find some sort of underground success in his life and celebrity fans like Matt Groening, Kurt Cobain, Tom Waits, Johnny Depp, etc. But his mental state has caused him a lot of problems over the years. For instance, almost killing his parents during a plane flight and being virtually unable to live without aid from other people.
The Dutch 2002 documentary Ramses Shaffy: Où est mon prince?, which is about Dutch singer Ramses Shaffy, is also heartbreaking. We see the aged singer destroyed by years of drugs and alcoholism, sometimes barely able to register what's going on around him. The last scene shows him singing "'t Is Stil in Amsterdam" ("It's quiet in Amsterdam") while accompanying himself on the piano. Near the end, he is crying, but still manages to finish the performance.
There are many in Ken Burns' The Civil War, but one that always stands out is the end of "Episode 7: Most Hallowed Ground", which tells the story of the birth of Arlington National Cemetery on Robert E. Lee's captured estate.
David McCullough: At one point [in 1864] the Union army was sending back 2,000 wounded, maimed, and dying men a week to Washington. Now the men Grant was sending to fight Robert E. Lee were being buried in Lee's own front yard. And that yard became Arlington National Cemetery, the Union's most hallowed ground.
Walking with Dinosaurs: At the end, when the meteorite hits. Same goes for when the same happens in Planet Dinosaur.