The last question thwarted us again and disproved my Guessability Theory.

What is the northernmost arm of the Mediterranean Sea?

What 1958 film is about a fan who'd sell his soul to aid the Washington Senators?

Who responded to Barry Goldwater's "In your heart you know he's right" slogan with "In your guts you know he's nuts"?

What song ranked #3 by Rolling Stone and #1 on its list of protest songs begins with the following lyrics?

"I was born by the river in a little tent
Oh, and just like the river, I've been running ever since"

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What's your Guessability Theory?
"The final answer is almost always something you could have guessed, even if you didn't." I guess that "almost" means it wasn't totally disproved, but it's a pretty good counter-example.
Ah, that does happen to me maybe half the time.