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Posted by Tim Harford

https://timharford.com/2025/11/the-silver-bullet-fallacy/

https://timharford.com/?p=9699

Is there a more annoying cliché in policy-wonk circles than “there are no silver bullets”? If so, it does not readily spring to mind. What those who intone this ritual phrase mean, of course, is not to expect too much. Silver bullets kill werewolves, we are told: just point, fire and forget. But those are fantasy tales. Real-life solutions are never quite as simple, are they?

Just pick your potential policy panacea: from microfinance to community currencies, wealth taxes to flat taxes to land value taxes, tool sharing apps to “nudges”, there is no shortage of ideas that somehow fail to reshape the world. Some of them have simply flopped, others have never won enough political support to be tried. Many work just fine, if in a quiet, understated sort of way. And quiet and understated is fine — provided you don’t expect a silver bullet.

Why, then, my irritation? Not just because the phrase “there are no silver bullets” is grotesquely overused, but because it misstates the difficulty. In fact there are plenty of silver bullets. The challenge is that not every problem we face is a werewolf.

The phrase “magic bullet” was coined by Paul Ehrlich, who won the Nobel Prize in Physiology or Medicine in 1908. Ehrlich’s aim was to find chemical compounds that would precisely target bacteria or other disease-causing microbes. He succeeded, discovering that arsphenamine was an effective treatment for syphilis. Penicillin and other antibiotics followed, offering a cure for bacterial infections that was little short of miraculous.

Alongside antibiotics, place vaccines: by priming the immune system with weakened or inactive fragments of a pathogen, vaccines have led to the eradication of smallpox and enormous progress against once-terrible diseases such as polio, measles and more recently Covid-19.

Or, for an example from the world of finance, consider the index fund. The idea was floated by the Nobel laureate Paul Samuelson in 1974, then launched in 1976 by John Bogle of Vanguard. Initially mocked as “Bogle’s folly”, un-American and mediocre by design, index funds are now enormously popular.

Each of these silver bullets downed a particular “werewolf” — a clearly visible, well-defined problem. Antibiotics targeted a common class of pathogens; vaccines recruited the body’s own immune system; the index fund allowed investors a way to make a diversified bet on the stock market without paying high fees to stockpickers of questionable skill. All of them work brilliantly. To say that there are no silver bullets is to do a disservice to the ingenuity of these ideas. Better to say that the difficulty is a lack of werewolves.

In 1973, two professors of design, Horst Rittel and Melvin Webber, published an article describing what they called “wicked problems”. Wicked problems, they argued, had a number of challenging characteristics. They defied clear description, lacked a “stopping rule” at which point the problem could be declared solved, tended to be contested, had few instructive parallels or analogues, and tended to be linked to or symptomatic of other problems. Most challenging of all, they resisted trial-and-error solutions because each experiment was a costly punt with significant real-world consequences for failure.

Examples of wicked problems include crime, climate change, inequality, the fall of birth rates or the rise of AI. When faced with a wicked problem such as these, expect people to disagree about what, if anything, the problem is. Expect solutions to be controversial, difficult to test, and at best provisional.

Not so with a werewolf problem. When there’s a werewolf stalking the neighbourhood, everyone can agree on the problem and on what a successful solution would look like. So go ahead and forge your silver bullet without shame. Don’t let anybody tell you that it will never exist.

Am I being pedantic in my choice of metaphor? Very well then, I am being pedantic in my choice of metaphor. But the distinction matters. When we mumble that there are no silver bullets, we’re implying that no attempt at any solution for any problem will ever really work. But that’s absurd. There are plenty of clearly defined problems worth solving.

This is true even when those clearly defined problems are surrounded by clusters of other problems. For example, antibiotics work spectacularly but within limits. Bacteria evolve resistance, which means we need incentives to develop, but not use, new classes of antibiotic. We also need to tackle the routine overuse of antibiotics, for example in rearing livestock. But these are distinct new problems for which distinct new solutions must be found. As antibiotics become less effective, shrugging and saying “there are no silver bullets” is no kind of response.

Vaccines, too, are a near-miraculous technology, but they only work if people are willing to be vaccinated. That’s not the kind of problem you can fire a silver bullet at. It requires patient, multidisciplinary work to understand the various reasons for reluctance and how we might respond to them. But are modern vaccines themselves a silver bullet? You can literally bet your life that they are.

As for index funds, there’s a simplicity to the idea that verges on genius. Samuelson gave Bogle the credit for an invention he ranked alongside “the wheel, the alphabet, Gutenberg printing, and wine and cheese: a mutual fund that never made Bogle rich but elevated the long-term returns of the mutual-fund owners. Something new under the sun”. That might be overstating the case, but index funds absolutely deliver on their goal of inexpensive, diversified investment.

Are they an investment panacea, though? Of course not. Index fund investors are as capable as anyone else of buying high and selling low, cowering in fear on the sidelines or scrambling to join a late-stage bubble. But to complain that index funds are not silver bullets is to misunderstand the nature of the werewolf that Bogle and Samuelson slew.

In the years since Rittel and Webber published their analysis of wicked problems, they have been much cited, and rightly so. Their formulation reminds us that there are certain kinds of problems that defy a clean, one-shot solution. But they do not deny the existence of problems for which solutions can be defined, tested and delivered.

We clever humans have managed to make silver bullet after silver bullet and slay werewolf after werewolf. So let’s not make the lazy mistake of believing that because some problems can never be fully solved, there is no such thing as a solution.

Written for and first published in the Financial Times on 16 Oct 2025.

I’m running the London Marathon in April in support of a very good cause. If you felt able to contribute something, I’d be extremely grateful.

https://timharford.com/2025/11/the-silver-bullet-fallacy/

https://timharford.com/?p=9699