A common trope in popular journalism is the "do you remember this guy?" article. Obviously a commonly-known person would not be a good subject, but less obviously the most-obscure person would also not be a good subject. If you write, "Have you ever heard of Babe Ruth?" everyone except Scotty Smalls knows who the Babe is. Readers will not be interested. But if you write, in a Field of Dreams-less world, "Have you ever heard of Moonlight Graham?" the answer is, "No, no one's ever heard of Moonlight Graham; the guy played right field for a half-inning of one game in 1905." Readers don't want to read articles that are designed to reveal the writer's superior knowledge. Especially when it very well could be the case that the writer didn't know about Moonlight Graham until a week ago, and now he's going around acting like the world's leading authority on all things Graham. The only exception is when the writer frames it from the perspective of "I didn't know this, either, until I recently accidentally found out."
So everyone knows is banal, and no one knows is pedantic. So how obscure can you go before it's too obscure? The Dennis Miller Ratio is still too obscure; instead of a lone smarmy writer, it creates an exclusive clique of the smarmy, but still a majority of the audience is left on the outside. What you want is something that appears obscure, that most readers or viewers believe is obscure, but which is, in fact, commonplace. Thus everyone remembers it but everyone feels like the possessor of exclusive knowledge.
How do you find something that everyone knows but no one knows that everyone knows it? It has to have once appeared important, so everyone knew it, but then turned out to be unimportant, so it is no longer relevant to popular culture. Like a number-one draft pick that didn't pan out (Ryan Leaf, Lawrence Phillips), a flash in the pan player predicted to accomplish much more than he eventually did (Josh Hamilton, Jeremy Lin), an actor who was going to be a star until his movies turned out to be bad (Josh Hartnett, Brendan Fraser), or a senator with an undistinguished career but who once was a presidential front-runner (Gary Hart, Paul Tsongas). Everyone feels proud of himself for knowing who these people are because he thinks most other people don't.