Humans are pretty smart. Apart from our special skill of wiping out large parts of our own population and several other species, we've achieved some pretty remarkable things.
But there's a lot. Like, a LOT of stuff that we still don't know. Some of it is surprisingly simple - the answer must be staring us in the face - and yet we just haven't worked it out yet. So here's our top five list of stuff we should know, but don't.
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