A classic 1950's-era science-fiction story tells of an alien invasion of Earth that goes horribly wrong. The invaders have highly advanced technology. They quickly knock down the terrestrial military, destroy governmental facilities, and eliminate all centrally organized resistance. But then disorganized resistance emerges: sabotage by creative, crafty humans that disrupts the alien forces and threatens to drive them away.
But this isn't your typical "Nyah, nyah, we homo sapiens are the smartest creatures in the cosmos" juvenile sf potboiler. An alien commander figures out that both sides — human and alien — need to work together, that each has much to offer the other. The invaders are from a slow, careful, methodical species. They built their civilization over æons, and it works. People are clearly quicker, more innovative, and more intellectually active. They're also more aggressive — as witness the history of humanity on this planet, written in blood and scarred with injustice.
The metaphor that the story proposes is that of a nuclear reactor. Humans are like U-235, the alien protagonist explains — they're the isotope of uranium that can split and give off extra neutrons as well as energy. The alien race is like the moderator that slows the neutrons down so they can react some more, or maybe like U-238, a nonfissionable isotope that can absorb neutrons and be slowly transformed into something active. Too little U-235 and a nuclear reactor doesn't work. Too much and it self-destructs in a runaway catastrophe.
This science-fiction story was a clever one, with a lesson that lodged in my mind for decades. Yesterday the tale surfaced as I read an op-ed piece in the local paper concerning college scholarships.
Why should somebody from a well-to-do family get subsidized to go to a university — especially to a public institution — just because s/he has high grades, good recommendations, intellectual brilliance, and so on? Shouldn't scholarships be allocated strictly on a need basis? Yesterday's essay in the paper argued in favor of that, based on the importance of helping poor kids move up in society, counterbalancing racism, and focusing assistance on those for whom it matters most. All good reasons, to be sure.
But there's a strong argument on the other side which the op-ed writer overlooked or chose to omit: better students make a school better. Like those atoms of U-235 in a nuclear reactor, it only takes a few percent enrichment to change the entire energy balance of the system. And good students don't simply encourage, directly and by example, better scholarship by their peers — good students also make for better teaching as they interact with and energize their professors. Smart undergraduates and grad students help a university attract stronger faculty members, who in turn attract stronger pupils in a positive feedback loop. (Fortunately this isn't a zero-sum game; better teaching in one generation makes for better teachers in the next.)
When I was in school I never thought about the faculty side of the equation, much less about the institution and its long-term health. Still farther from my consciousness were larger questions of how society can encourage learning and intellectual progress. A few merit-based scholarships, to keep some of the best kids from going far afield to school, may turn out to be one of the smartest investments that a community can make in its future.
(Some research suggests that the story I remembered was an anthologized version of the novelette "Pandora's Planet" by Christopher Anvil, originally published in Astounding magazine in September 1956. See  for what may be the text, Chapter 1 of Pandora's Legions published by Baen Books (see FreeLibrary (29 May 2003)). See also OnePerScore (6 Feb 2000), SummaCumLaude (27 May 2001), UniversitiesAndRace (29 Jun 2003), ... )