When I was a child, I believed that in Heaven, everyone would know everything. All that science had yet to uncover, all the things science couldn't uncover because the evidence wasn't preserved, what happened on the Mary Celeste - everything. I don't remember developing or constructing this idea in my head, it's just my earliest memory of what I thought Heaven would be. My vision of a reward for a good life was an afterlife spent learning everything there is to know. I feel I should say something like "which probably explains a lot," but "which makes absolute sense, all things considered," is probably more accurate.
(I also thought that every person's whole life would be recorded, like a script, so that everyone who had ever known me would be able to read every embarrassing thought that had ever crossed my mind, every mean things I had said when I thought no-one could hear, and all my heinous crimes, like cheating on that question on a test three months ago. I think children picture the afterlife as "Like this one, but better," and apparently I just assumed the shame would carry over.)
It was rather a let-down to learn that what the religion I was raised in meant by Heaven was the joy of being in God's company forever. That seemed awfully dull by comparison, and probably made the probable non-existence of Heaven less of a loss.
Today, the book I'm currently reading noted that there isn't sufficient preserved evidence for archaeologists to determine whether ancestral humans had done away with Neanderthals by violence, or if they had edged them out through superior technology and ability to exploit the land. I was struck by the pity of the fact that no-one will ever know. And then a reassuring, incomplete thought came to me: "At least we'll find out when we're dead."
I think this particular incident was pretty funny because it was a harmless, childish view, but it does highlight how deep-rooted ideas can be - even those which are baseless and ridiculous under the slightest scrutiny. It's also why when someone says that it's alright for them to use that word or make that joke because they don't really mean it, they're not like that, I don't believe them for a second, even - especially - if they believe it of themselves.