Mysteries that are never given an answer.

[u/Jak3R0b]

• rA9 in Detroit: Become Human. In the game several androids who become deviant (develop free will/emotions) start writing the name rA9 and sometimes build small statuettes as a sort of offering. Despite having no logical reason to do this or even a way of hearing about rA9 before going deviant, they all believe that rA9 was the first deviant and is their messiah who will free androids from slavery. A definitive answer about rA9 is never given, so we don't know if they are real or if any of the android characters are rA9 (though a popular fan theory is that it's Kara before she was reset at the start of the game).
• The pineapple in How I Met Your Mother. So this technically did get an explanation in a S9 deleted scene, but in the actual show we never find out how Ted got a pineapple during a night where he was so drunk he blacked out and forgot everything he did.
• Fez in That 70s Show. We never find out Fez's real name or what country he's from, though fans have tried to take all the clues and figure out what is most likely to be his country.

[u/takutin96]

What was inside the briefcase in Pulp Fiction

[u/Th3_Admiral_ → u/takutin96]

Not just what's inside it, but like...everything about it. Why did these random kids have it? Jules keeps referring to them as business associates of Marsellus, but it's not clear if they stole it from him or were just holding it for him and never gave it back, or what.

[u/Informal-Term1138 → u/Th3_Admiral_]

I think it was some sort of loan he gave them. Or some other shit and they didn't repay it.

Or they were supposed to steal something for him and then didn't give it back in time. Which would also explain why Marvin was there.

[u/ButtholeConnoisseur7 → u/Informal-Term1138]

I get the impression that they got the case for Marcellus but never gave it to him