It was born out of a mistranslation and has been misused ever since....but let us do a little thought experiment first:
Let's say you are a scientist and you noticed a phenomenon you would like to tell the world about. "The brain...", you say, "... can listen to a conversation and make sense of the frequencies, decode them into symbols and meaning... but when it is confronted with two such conversations simultaneously, it cannot deal with both threads in parallel. At best it can try to switch back and forth quickly, trying to keep up with the information."
So much for your theory—you formulate your findings and share it with colleagues, it gets argued and debated, just as it should be.
But now something odd happens: while all your discussions were in English, and you wrote it in English, and despite the fact that a large percentage of the leading scientists and Nobel Laureates are English speaking...somehow the prevailing language for publication is....Mongolian! There is a group in Ulaan Baatar, merrily taking your findings with great interest and your whole theory shows up all over the place...in Mongolian.
But here is the catch: you wrote that it is not possible to listen to two conversations at the same time, and thus their meaning to you is, well, undefined, until you decide to follow one of them properly.
However, as it turns out, Mongolian has no such word—"undefined"! Instead it got translated with an entirely different term: "uncertain", and the general interpretation of your theory has suddenly mutated from "one or the other of two conversations will be unknown to you" to the rather distinctly altered interpretation "you can listen to one, but the other will be.....entirely meaningless".
Saying that I am "unable to understand" both of them properly is one thing, but... my inability to perceive it does not render each of the conversations suddenly "meaningless", does it?
All of this is of course just an analogy. But it is pretty close to exactly what did happen—just the other way round: the scientist was Werner Heisenberg.
His observation was not about listening to simultaneous conversations but measuring the exact position and momentum of a physical system, which he described as impossible to determine at the same time. And while he discussed this with numerous colleagues in German—Einstein, Pauli, Schrödinger, Bohr, Lorentz, Born, Planck—just to name some of the Solvay Conference group of 1927—the big step came in the publication in English, and there is "the Mongolian" in our analogy!
Originally Heisenberg wrote it as "Unschärfe Relation"—that transliterates to "Unsharpness Relationship"—but as there is really no such term in English ('blurred', 'fuzzy', 'vague' or 'ambiguous' have all been tried), the translation ended up as "the Uncertainty Principle"—when he had not used either term at all (some point to Eddington). And what followed is really quite close to the analogy as well: rather than stating that either position or momentum are "as yet undetermined", it became common usage and popular wisdom to jump to the conclusion that there is complete "uncertainty" at the fundamental level of physics, and nature, even free will and the universe as such. Laplace's Demon killed as collateral damage (obviously his days were numbered anyway....)
Einstein remained skeptical his entire life: to him the "Unbestimmtheit" (Indeterminacy) was on the part of the observer: not realizing certain aspects of nature at this stage in our knowledge—rather than proof that nature itself is fundamentally undetermined and uncertain. In particular implications like the "Fernwirkung" (action at a distance) appeared to him "spukhaft" (spooky, eerie). But even in the days of quantum computing, qbits and tunnelling effects, I still would not want to bet against Albert ;) His intuitive grasp of nature survived so many critics and waves of counter-proof ended up counter-counter-proved.
And while there is plenty of reason to defend Heisenbergs findings, it is sad to see such a profound meme in popular science, which is merely based on a loose attitude towards translation ( and there are many other such cases...). I would love to encourage writers in French or Swedish or Arabic to point out the idiosyncracies and unique value of those languages—not for semantic pedantry but the benefit of alternate approaches.
German is not just good for Fahrvergnügen, Weltanschauung & Zeitgeist, there are many wonderful subtle shades of meaning. It is like a different tool to apply to thinking—and that's a good thing: a great hammer is a terrible saw.