I'm always looking for metaphors that carry a visceral punch to a general audience when conveying what I perceive to be an important truth about some technical issue.
Here are two for blockchains.
The King turned to Tom, and said kindly—"My poor boy, how was it that you could remember where I hid the Seal when I could not remember it myself?"
"Ah, my King, that was easy, since I used it divers days."
"Used it—yet could not explain where it was?"
"I did not know it was THAT they wanted. They did not describe it, your Majesty."
"Then how used you it?"
The red blood began to steal up into Tom's cheeks, and he dropped his eyes and was silent.
"Speak up, good lad, and fear nothing," said the King. "How used you the Great Seal of England?"
Tom stammered a moment, in a pathetic confusion, then got it out—
"To crack nuts with!"
Just to belabor the point, I contend that blockchains are beautiful, complex, and useful in very well-defined circumstances ... but that many of the uses proposed for them do not take advantage of their intricate beauty and special properties. Instead, I contend that most of these uses simply apply them as a blunt instrument.
This is better than the old "to someone with a hammer, everything looks like a nail" adage. Twain's version, "to a hungry person with a nut, everything looks like a nutcracker," is actually backward from the hammer one — and would be a step up in the blockchain context, because Twain at least starts from the problem (hunger).
Another metaphor I like is based on the Dutch Tulip mania of the early 17th century. This is the well-known story of when the market for tulip bulbs somehow went berserk over just a few years, and things which were, yes, fairly beautiful, somehow came to command unreasonably enormous prices. And then, just as quickly, the price collapsed.
Two lasts of wheat
Four lasts of rye
Four fat oxen
Eight fat swine
Twelve fat sheep
Two hogsheads of wine
Four tuns of beer
Two tuns of butter
1,000 lbs. of cheese
A complete bed
A suit of clothes
A silver drinking cup
This seems to be a painfully apt metaphor for cryptocurrencies, but I contend that it applies equally well to many of the beautiful yet, ultimately, absurd business models which have sprung up in the area of fintech and blockchain applications in general.
One lesson we might learn from this story that exchanging great value — such as 1,000 lbs. of cheese or many thousands of dollars — for something beautiful but ephemeral and somewhat intangible — like a flower or a bit of data (maybe a few bytes which, when appended to an existing data block, ensures that the augmented block has a SHA256 hash with a certain number of trailing zeros) — is a action which only makes sense in a particular social context. But that context might well disappear overnight as some social/financial bubble pops.
There's another thing we might learn from this story. I was in Hollard recently and took a train from Amsterdam airport to Eindhoven. Along the way, we rolled past many large, beautifully tended, brightly colored, rectangular fields — of tulips! During the tulip mania of the 17th century it would have been insane to invest your life's savings in tulip production hoping to become enormously wealthy. Surely during that bubble, a few people made or lost a ton of money while most lost a modest amount. But apparently the tulip bubble left a long shadow in history in the form of a productive flower industry that exists, in a very different form, even today.
[Of course, I do not know for a fact that today's flower industry in The Netherlands is in any way the direct result of the 17th century tulip mania: flowers might have always been a Dutch industry and in fact perhaps the tulip mania could have been a detriment to that industry, rather than a benefit. Still, it is nice to imagine that today's bloemenindustrie is the silver lining of that dark cloud from centuries ago.]
A boneheadedly bad idea like tulip mania or "put everything on the blockchain" may leave behind not only some rich grifters and many impoverished suckers, but also, accidentally, a little positive change in the world. For tulip mania, it might be today's flower industry. For blockchain mania, I have always hoped it would be a wider understanding of the importance of a solid PKI (for the definition of which, see the IHE article page on this site). Or maybe, more modestly, just an increased awareness of the importance and utility of some ideas in cybersecurity.