Well there's a long-held believe down the drain. Of course you can pair wine with whatever the hell you want but it seems that pairing chocolate and red wine does a disservice to both. Serious Eats breaks down the reasons why they don't work together as well as suggesting the types of chocolates that work with specific wines. (Hint: Port.)
Here's why the combination of red wine and chocolate is never going to truly taste good. Sugar. A sip of dry red wine without any perceptible sweetness will turn bitter and sour when taken with sweetened chocolate. Unless you're munching on plain roasted cocoa nibs, back away from the Cabernet, please.
Pairing wine and chocolate isn't hard, though—look for a wine with some sweetness, and the whole thing can come together beautifully. Don't let the word "sweetness" or the phrase "dessert wine" scare you away. We're not talking about wine coolers here. A proper dessert wine, when paired with a sweet food, will taste less sweet than it might on its own. Think of the wine as the raspberry syrup drizzled across your molten chocolate cake: it adds the contrasting flavor to make the chocolate pop.