WWII Naval pilot Joseph P. Kennedy, eldest brother of John F. Kennedy, volunteered for Operation Aphrodite, a dangerous series of 1944 missions to destroy hard-to-reach targets like the German V3 supercannon. He and his co-pilot were to arm the explosives in their bomber, which could not be done remotely, and bail out. The bomber would then be piloted by remote-control, crashing into the V3's bunker complex and exploding. But shortly after the explosives were armed, they prematurely exploded, vaporizing plane and crew. The shaggy dog was thoroughly shot, however, when it was later discovered that the V3 complex had already been damaged beyond repair with a more conventional method by Lancaster bombers from the 617 Squadron on July 6, 1944.
Roman Emperor Heraclitus' entire life was this. He rose from relative obscurity to depose the tyrannical and insane Emperor Phocas, who had lost most of the Roman Empire to the Sassinid Iranians. Heraclitus retook Anatolia, Syria and Egypt through years of hard fighting, personally leading his armies and fighting Persian cataphracts hand to hand. Eventually the Persians made peace and became a subordinate ally after Heraclitus took their Capitol. Less than six years after peace was delayed, the newly converted-to-Islam Arabs invaded and conquered almost everything Heraclitus had retaken.
The July 20th Plot was one of the many desperate attempts by sane Germans disgusted by Hitler and the Third Reich during World War II. As with earlier attempts, the plan was within inches of killing Der Fuhrer and failed only due to the combination of a cavalcade of improbably unfortunate twists of fate. Conceived and coordinated by Henning von Tresckow, planned and carried out in large part by the charismatic one-eyed and one-handed Major Claus Philipp Maria Justinian Schenk Graf von Stauffenberg, Brigadier-General Hans Oster, General Friedrich Olbricht, and young Oberleutnant Werner Karl von Haeften, all of whom (along with many, many, many others who were crucial to the plot) paid for their attempt with their lives - and many of them paid with the lives of their families and friends. Valkyrie tells much of the story.
The Vietnam War veterans were looked down upon at the time of their return. To make it worse, in 1975 after the Americans left Vietnam, the Communist Northern side quickly steamrolled over the Southern side that the US sided with. Making the entire conflict and casualties on the American side ultimately meaningless.
There's the Second (Third if you count its war with France) Vietnam War of 1979 between Vietnam, Cambodia and China 4 years later, especially meaningless for China and the CIA. China went to help the revolution in Cambodia because of an American "suggestion", which evolved into a war between the Khmer Rouge and Vietnam, flattered the industry and trust it had built in North Vietnam before during the last war, only for the Khmer Rouge to fall. Oh, and small-scale fighting continued until 1990.
Even worst: the Soviet war in Afghanistan in the 80s. Thousands of Soviet casualties to try to force communism on Afghanistan... just for the whole communist and Soviet system to come crashing down a few years later!
More like reinforced. The only reason they ended up there was because a brand new communist regime trying to control the country invited them.
What's more, in order to combat the Soviets the US funded resistance armies to oppose them...who later became Al-Qaida, sowing the seeds for 9/11.
Another film-making example, the documentary Lost in La Mancha was intended to be a behind-the-scenes of the Terry Gilliam movie The Man Who Killed Don Quixote. It didn't go as planned. In fact, at certain points in the documentary, it almost seems as if God Himself doesn't want this movie made. On the other hand, recent rumors suggest this may someday soon be averted.
Cosmonaut Vladimir Komarov in the Soyuz 1 space mission, during the Space Race. Komarov knew the mission was unsafe, but knowing that his friend Yuri Gagarin was his backup, went ahead with the mission anyway so that his friend wouldn't have to take the risk instead. Everything went wrong. The capsule's solar cells didn't deploy properly. Communications broke down. The manoeuvrings thrusters that were designed to re-orient the ship lacked pressure. He couldn't see the sun to navigate the ship. After all that, after a heroic effect rigging up a system with the gyroscopes so that at last he could re-enter the atmosphere, the parachutes failed, and he died. Within a year, his friend would die in a plane crash anyway.
The entire Universe will eventually give way to entropy. The aversion is Dyson's eternal intelligence hypothesis (or whatever you'd term "God"), and, of course, the possibilities of The Multiverse.
In North Carolina, a pregnant mother on her way to give birth was killed in a car crash, but the baby survived and was delivered successfully. This amazing story got attention in the news, but the baby died a few days later.
The would-be second Iranian 'revolution' died with a whimper. After the dubious reelection of Mahmoud Ahmadinejad in 2009, protests broke out across the country on a scale not seen since 1979, inspiring hope both within and without Iran that real change was possible. Alas, the protestor's aspirations were nipped in the bud, with deadly force.