What it is:
A man walks into a bar, sits down, looks at the bartender, (who is standing in front of an assortment of taps and bottles), and says "I'll have a beer, please." And then, astonishingly enough, the bartender hands him a beer. Just a beer, just the idea of beer, the perfect manifestation of beer, as a concept, in a glass. That's like walking into a restaurant and ordering "a sandwich," or telling a store owner "I'll take six candies, please!"
"Two meats, one of your vegetables and eight foods, my good man!"
I used to tend bar, and if anyone ever walked in and asked for "a beer," they'd get a nice, cold glass of "I'm not moving until you make a goddamned choice." Beer isn't like water or milk. There are lots of different brands of beer and, broader than that, lots of different kinds of beer; light beer, dark beer, ales, lagers, IPAs, whatever. And when a bartender pulls "a beer" out from wherever, what is he even handing over? Should we assume, of all his beers, that that one is the... beeriest? It is the most beer-like of all the beers?
Why it Happens:
Mentioning a brand by name requires tricky advertisement negotiating, and simply inventing a fake beer name for a movie requires tricky creativity, and neither of these are things that modern filmmakers want to trouble themselves with. So, to make everyone's lives easier, I've taken it upon myself to create a new beer, called beer, that comes in one flavor, (beer), and it's made by Beer Company in the Beernited States of Beermerica. Any director can feature this product in their movie, free of charge.
Finally, a beer emerges on the market with that smooth Beer taste, but none of the hassle of character! Also available in an unlabeled, tinted bottle or comically giant jug with X's printed on it. Remember, just look for the beer with the slogan "Beer beer? Beeeeeer!"
What it is:
We see a couple of best friends sitting around their apartment, depressed. They've both recently been fired, they're late on their rent payments and they've got student loans out the ass. All they have is their music, but that won't pay the bills. They're about two weeks away from getting kicked out of their apartment and right as they're openly wondering how they're going to get out of this mess, they turn on the TV at the exact moment that an MTV personality is announcing a local Battle of the Bands with a grand prize of holy shit your rent money and student loans!
Or a mother is cleaning her kitchen, idly wondering where her wacky, rambunctious son is, when the TV comes to life, already tuned to the news. "Where's that wild boy of mine" is almost overlapped by the news anchor alerting us that "This just in, local boy broke into zoo and freed all of the animals, and boy it sure was zany and unpredictable. If I were the mother of this boy, I'd probably drop a plate in the kitchen and then comically faint due to the shock."
Then that would happen.
Why it Happens:
Because the people who run movies are terrible and they have no faith in you. They can't just show you characters in trouble, they need to have the characters explicitly say "We need money" or "We need jobs" or "We need to find our friend." And they can't have the answer appear casually in the background, they need to smash cut to the TV and spell out a solution just seconds after a problem is stated, because they think you're incapable of retaining any single piece of information for more than a second, because they think your brain is goldfish.
Sick of not having your answers conveniently broadcast directly to your face immediately after you run into trouble? Worry no more! Our chief scientist, Daniel O'Brien, recently discovered a way to read minds, and he refused to use the technology on anything except televisions. For you! Every TV comes with 900 channels and a fairly invasive satellite that uses a complex mixture of radiation and tumors to scan your brain functions. Whenever it notices a problem or, really, any thought you have, the TV will turn on and instantly switch to a channel that is handling something relevant to your current thought! (If no program is covering your specific problem, the machine will self-destruct.) The time of actively thinking about ways to solve your problems is over! Do this other thing now!