There's something compelling about a story with no definitive answers. It's no wonder a lot of our favorite works of fiction have an element of mystery, and in some of them, the loose ends are never completely tied up. Think of how many of our spooky Tales Around A Campfire end with a line like, "... and no one ever found out what happened to the missing teenagers."
In real life, though, unsolved mysteries have a way of inviting wild speculation, usually based on evidence for which even the word "slim" is an overstatement. Consider, for example, the off-the-rails "explanations" people came up with to account for the fact that even powerful telescopes couldn't see any surface detail on the planet Venus. Here's how Carl Sagan described one of these lines of thought, in the episode "Heaven and Hell" of his wonderful series Cosmos:
I can’t see a thing on the surface of Venus. Why not? Because it’s covered with a dense layer of clouds. Well, what are clouds made of? Water, of course. Therefore, Venus must have an awful lot of water on it. Therefore, the surface must be wet. Well, if the surface is wet, it’s probably a swamp. If there’s a swamp, there’s ferns. If there’s ferns, maybe there’s even dinosaurs.Observation: I can't see a thing. Conclusion: dinosaurs.
- the Bermuda Triangle has opened a branch office in the Indian Ocean, and the crew went through a portal to parts unknown
- the crew were abducted by aliens
- the ship got too close to an island run by the Illuminati, so the crew had to be eliminated
- the ship was attacked, and the crew eaten, by (choose one): a giant squid, a marine version of the Loch Ness Monster, beings from Atlantis, Cthulhu