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Peter Lynch famously told investors to "buy what you know" -- that is, to invest in the companies that made what they personally used and liked. But Lynch wasn't afraid to rely on the intuition of people he knew and trusted when they found something in the marketplace that they simply loved: It was Lynch's wife who clued him in to the appeal of L'Eggs pantyhose. (Or at least that's how Lynch tells the story.)

Unfortunately, it's not always so easy to find someone who can so smartly assess the appeal of something you don't personally know much about. How, for example, can we make sense of new technologies when we aren't even remotely in the demographic these new new things are aimed at? (It would be a bit like asking grandpa to evaluate the appeal of the Jonas Brothers.)

Some recent research out of Morgan Stanley attempts to answer the question of what the kids are into when it comes to media and technology by doing something that seems so obvious that it's a wonder no one tried it before: They asked a kid. Specifically, Morgan Stanley's European media analysts turned to a 15-year-old intern to explain just how British teens make use of all their new media options. And when the intern, Matthew Robson, turned in a report that actually made more sense than a lot of adult-penned investment bank research, they went ahead and published it.

It's hard not to be reminded of one memorable scene from the Depression-era classic Duck Soup: Groucho Marx is handed a baffling financial report. "A four-year-old child could understand this," he declares, before turning to his assistant and adding, in a stage whisper, "Run out and find me a four-year-old child, I can't make head or tail out of it."

Is Robson's report worth reading? Well, yeah. Robson's a sharp kid, with some interesting observations: he's fond of Facebook, for example, but down on Twitter, because British teens evidently prefer to use their phone credits not to twitter but to directly text their friends. On his "hot" list: "Really big tellies," iPhones, and "anything with a touch screen." On the "not" list: "Anything with wires." Robson also declares that old-fashioned paper Yellow Pages are useless to teens because they "contain listings for builders and florists, which are services that teenagers do not require."

Is the report a useful guide for investors? Well, here's where it gets a bit more tricky. It's clearly more useful for British investors than American ones, since a lot of the specific issues it raises don't really apply in the US. But more importantly, it doesn't actually attempt to assess any individual companies or stocks.

When Lynch invested in companies he "knew," he only did so after getting to know not only their products but also their balance sheets pretty personally. Investing in what you "know" -- or what someone else with good gut instincts tells you about -- is a lot harder than it looks, which is why so few people who read Lynch's legendary investment manuals managed to score anywhere near as many ten-baggers as Lynch himself by investing in things they thought they "knew."