History is more or less bunk. It's tradition.
— Henry Ford — 1916-May-25 — Chicago Tribune
During part of 1941 and 1942, when the Luftwaffe was busy in Russia, the German radio regaled its home audience with stories of devastating air raids on London. Now, we are aware that those raids did not happen. But what use would our knowledge be if the Germans conquered Britain? For the purpose of a future historian, did those raids happen, or didn't they? The answer is: If Hitler survives, they happened, and if he falls they didn't happen. So with innumerable other events of the past ten or twenty years. Is the Protocols of the Elders of Zion a genuine document? Did Trotsky plot with the Nazis? How many German aeroplanes were shot down in the Battle of Britain? Does Europe welcome the New Order? In no case do you get one answer which is universally accepted because it is true: in each case you get a number of totally incompatible answers, one of which is finally adopted as the result of a physical struggle. History is written by the winners.
— George Orwell — 1944-Feb-04 —As I Please
90% of everything you know is false.
At the beginning of the 20th century, it was commonly believed that airplanes were impossible, that atoms were the ultimate particle, that there were only 8 planets, that herbal medicines were ignorant superstition, that cornflakes suppress sexual feelings, that drowning victims could be saved by rolling them on a barrel, and that women were inferiors, without the right to vote.
By the end of the 20th century, we knew better: airplanes fly everywhere, there are hundreds of known subatomic particles, Pluto was discovered in 1930, the pharmaceutical industry investigates tropical plants for their possible use as drugs, cornflakes are a tasty breakfast cereal, we know how to perform CPR, and women are persons.
So much information that we accepted as common truth simply turned out to be wrong. During this same century, various theories arose, were at first rejected as obvious fantasy, and then were eventually accepted as true (e.g. continental drift, global disasters, mass extinctions).
The amount of ignorance in the year 1900 was amazing. Yet less than a decade into the 21st century, we're already rejecting truths of only 10 years ago. Pluto isn't really a planet, and countless people died because we did CPR wrong, spending far too much time on breathing and not enough on circulation.
Ideas that promised salvation came and went. Marx's thoughts on communism offered freedom for the working man but led to decades of oppressive governments. Darwin's theory of evolution was used to justify eugenics until its ultimate implementation by the Nazis. Freud's psychology theories revolutionized the mental health field, but have now largely fallen out of favour.
Other theories arose during the 20th century that are still accepted in popular opinion even though these convenient untruths have long since been rejected again by science (e.g. atoms have planetary orbiting electrons, lemmings are suicidal, a Blue Moon is the second full moon in a calendar month, and styrofoam cups are environmentally worse than paper cups).
Meanwhile, the news media do more than simply report the news. Since the beginning of this century, American citizens have been put into a state of fear of terrorist activities. But why now, as compared to say in the year 1969 when it wasn't considered a problem that the United States experienced dozens of plane hijackings and three thousand terrorist bombings, most of which were reported only as local news.
History books aren't static; newly discovered truths and insights are continually being incorporated in ways that would make Winston Smith's Records Department at the Ministry of Truth proud.
The eugenics movement, justified by Darwin's theories of the survival of the fittest was supported by governments and academics around the world. American institutions sponsored eugenics research in Germany right up until the Nazi Holocaust, after which everyone, including most historians, tended to completely forget about it.
Some events, such as President Kennedy's assassination, have been thoroughly investigated, researched, and studied countless times, and even so there are serious doubts about what actually happened. So how much faith should we have as to the truth of news reports of events that have had far less scrutiny? Generally the only reason we accept news reports that fit well with our view of the world is precisely because they haven't been well investigated.
Some religions teach that we are in the final generation of humanity and that supernatural forces will soon intercede, so it might not be unreasonable for some of their members to think that this generation is in the process of learning the world's final truths.
But most people don't hold such beliefs, and for them it isn't at all reasonable to think the current generation is somehow special. It isn't reasonable to imagine that a century from now history won't regard us as quaint and ignorant, believing so many things that are silly and obviously not true.
It's almost certain that much of what we believe now is untrue, and it's only that the majority of us share the same set of common false beliefs that conveniently keeps us sane and allows society to function.