I don’t think that I believe that I’m right. But I’m probably wrong about that.
I’m pretty sure I’m wrong about this.
There was some study cited on BBC Radio the other day where a bunch of test subjects were given a sweater to handle. They were then told (untruthfully) that the sweater had been owned by a murderer, and the vast majority freaked out and had a bad feeling about it - regardless of spiritual belief.
That’s pretty dumb on the face of things, that to pretty much everyone in the world, an inanimate object would possess some kind of magical power due to its provenance.
OK. Twenty five years then. Or whenever the story broke, less a month. My point was concerning the sort of out-of-nowhere, we never thought of that before, nature of the event when it happened.
I rest my case. 
Actually, this is an interesting approach which can easily be run with more effectively with a different example. Like, two thousand years ago nobody suspected that lightning was made of discrete particles. Also suspected that the sun was made of burning air. And so on.
I think it’s a stretch to assume (as you’re doing) that people project a supernatural quality on an inanimate object. Some people simply have a visceral reaction to things by association.
If you were to insist that I hold a knife you claimed was used in the Sharon Tate murders, I’d resist–not because I think some kind of evil mojo is in the knife that I might catch like the cooties. It’d be because being in proximity of something assocated with an evil act (like murder) can be creepy. Would it bother you if the previous residents of your home died in a murder-suicide? It would for a lot of people, because the association with something tactile is so strong.
Now, maybe the “killer” didn’t use the sweater in his killings, but clothes are still a very personal thing–they contain DNA, retain smells of the previous owner. “Knowing” something that personal was once owned by a an evil person can cause a visceral reaction much stronger than if you handed me the murderer’s copy of USA Today.
We believe that death is inevitable.
In this vein. No one really knows what’s at Earth’s core, because Earth’s mantle is opaque to us. It may be something we’ve never imagined.
I apologize if I am hijacking this thread, but I think the best way to go about answering this question is to look at it from a more broadly social perspective of knowledge. That is, what in the standard understanding of the world is almost certainly wrong? Or, what in the standard understanding of the well educated is almost certainly wrong? What are the general assumptions about the world, both physical and social, that will be overturned in the future? Or, what are the things that people in the future will think were appalling or idiotic in our society?
In my studies of eighteenth-century materialist philosophy (part of the subject of my dissertation), I find, from my twenty-first century perspective, the oddest sorts of juxtapositions: People who adamantly insist on the equality of all men, while considering women to be more or less furniture. People who have surprisingly well-developed ideas on how environment and temperament determine human behavior, who nevertheless maintain that all matter reduces to one of the four elements. People who support the idea that, within certain constraints, people should govern themselves, who offer nothing but a constitutional monarchy as a form of government. And so on.
Over the past two hundred years, each of these blinders have been lifted—albeit not entirely in practice—with new scientific discoveries and new social mores. However, neither the equality of women, nor the possibility of more than four elements, nor democracy were unheard of in the eighteenth century or even millennia before then.
So with that in mind, I would say that the commonly accepted idea most likely to change over the next fifty or hundred years or so, would be (someone has already mentioned it, I believe) the understanding of human consciousness and intelligence. I base this claim on two observations. First, research in artificial intelligence. I am thinking specifically of the Chinese room experiment and what is known as the “ghost in the machine.” Each of these offers insight into what human intelligence is, mostly by showing what it cannot be. Second, advances in medicine. Especially with people in permanently unconscious states, there have been problems deciding when it is acceptable to let them die, or more broadly, when it is acceptable to choose the time of one’s own death. As people live longer, but in more pain and with lower mobility, this question will become part of more people’s lives, both for themselves and as they address their parents’ and grandparents’ mortality.
The changing philosophical and scientific understanding of what goes on in our bodies combined with an increasing need to deal with it will, I offer, drastically change what it means to live and what we think we are. The idea of man as a machine, is, of course, far from new (it was the title of a work by La Mettrie published in 1848), but I think that it will become far more prevalent, especially in day-to-day situations, where it is currently more or less absent. You will notice that I offer no ideas on what those changes might be. And that is because I don’t know. It would take months, years probably, to formulate a guess. Perhaps someone has already done so.
As far as less social things go, I have no ideas as to what we don’t know. My guess is that in the future, we’ll figure out what dark matter is. If we go with the idea (also previously mentioned, if I’m not mistaken) that the reasoning as well as the conclusion must be right, I’m pretty sure that what everyone currently has to say about dark matter will turn out to be wrong or at the very least, woefully incomplete.
Oh no, I don’t think I exist. Go on, prove me wrong.
Why, did you think I was right? 
But do tell me what’s thinking!
My first thought in response to “what are we all wrong about” is that old gem “All that is necessary for the triumph of evil is that good men do nothing”
Everyone seems to agree with this, but if you think about it, it makes no sense at all.
Of course it’s still invalid as an answer since at the very least I know it’s not true, and everyone includes me too, even if everyone else is wrong about it. Even beyond that It’s highly unlikely that there isn’t anyone else in the world who agrees with me on this… I just haven’t found them (but then I haven’t really looked) just out of curiosity… can anyone else point me to an example of a prominent author or philosopher who’s taken a stance against this oft repeated misinformation??
I think AdmiralCrunch’s answer is probably the closest thing you’re gonna get to a correct answer. Even though many of us know the idea of ‘Free Will’ makes no sense, the way our brains work pretty much forces us to see ourselves as having this magical property, and act as if it were real, thus making is all wrong about it.
…and now to hijack:
That’s actually something I’ve thought about many times. Though I think you’re slightly off the mark in 2 ways.
1st
I think consciousness, by most people’s definition, is something that requires memory. I guess I’m really only arguing with your choice of words on that part, I think I know what you mean anyway. I would just say that inanimate matter ‘experiences’ its own existence, and to some limited degree, experiences the world around it.
2nd
Who says inanimate matter doesn’t have memory? It’s affected by it’s environment in lasting ways, and that means it stores information to at least some degree. A CD is inanimate… yet it clearly stores information! I would say that what makes our experience of the world different from that of inanimate matter is something more along the lines of the ability process information. Recalling information which has been stored, and comparing it to other experiences.
A negative number times a negative number is actually negative, not positive. Remember how you kind of rolled your eyes at this one upon first “learning” it, but were too young to argue about it? The actual proof requires the use of hypergeometric functions and group theory, but the result is intuitive.
Also, the arcsine really is just one over the sine. This was known hundreds of years ago and is preserved in the notation sin^(-1), but the knowledge was lost when Frederick the Great, in an episode of comic miscommunication, arranged for the authorship of a standard mathematics textbook by a shepherd from Gilgenburg and simultaneously hired Leonhard Euler to design an improved sheep shear. As an historical aside, Euler did a pretty good job on the sheep shear project.
And finally, while you do have to add a constant when evaluating an indefinite integral, it turns out that the constant is always 12.
I plan to provide a detailed discussion of this in my upcoming book Obtuse Triangles: A Journey Through Mathematical Incompetence.
Now obviously what Der Trihs says, only in this instance of course excluding all other pronouncements, is correct.
So to answer the OP we have to find something that we all believe that we could then disprove.
That eliminates any subject that is the common subject of discussion so we need some opinion that is so obvious that no-one ever talks about it. So nothing that requires any opinion or knowledge or sentience.
That means if I propose something we all agree on and no-one can refute it then it becomes the “What are we all wrong about?” of the OP and we must disprove it.
So I suggest We Are All Alive
By this I only refer to those of us posting to the thread. Of course if a self confessed zombie Doper were to post to this thread we would need another principle to refute.
Posting in this thread. To feel alive.
I’d change “exists” to “is real”. But yeah.
Kobal 2 didn’t claim to be thinking!
Everybody thinks glass is a liquid, an amorphous solid, or a solid. It’s really imaginary. Even I don’t think that’s true.