“So the thing you have to understand is this is radio,” says the voice in the darkness — a little bit squeaky, a little bit nasal, not at all the voice you’d assign to the leader of a benign radio cult if it weren't already so familiar.

Ira Glass, creator and host of the weekly public radio story anthology This American Life, begins all his speaking engagements this way. That opening line is always good for a laugh. But at GW Lisner Auditorium Saturday night, Glass kept his audience in the dark for the first few moments while he riffed on the sense of intimacy that makes radio such a powerful storytelling medium. It was a memorable beginning to an inspiring two-hour discussion of the techniques of storytelling as practiced by the staff of This American Life, and the reasons stories are so indispensable to our humanity.

While the opening-in-the-dark gimmick is a fixture, what he says to his even-more-captive-than-usual audience after depriving them of their sight is always a little different. Keeping the lights off, he played tape of a female teenage gang member he’d recorded in his days as a National Public Radio reporter in Chicago. Describing a frightening encounter with the wrong end of a gun, the girl’s voice was achingly expressive and vulnerable and human. Glass said he'd often felt grateful his audience couldn’t see the gangbangers, because he knew that if the Morning Edition crowd got an eyeful of their tattoos and black lipstick and hard stares they’d never have heard what these girls were saying.

The lights eventually came up to reveal Glass, suited and bespectacled, seated behind a desk with a few pages of notes, a mixer, and two CD players — one loaded with interview clips, he told us, the other with music. Sometimes in the instant before triggering a sound cue, he would allow one of his hands to soar briefly over his head, like an orchestra conductor calling in the string section. After that lights-out demonstration of radio’s power, Glass observed that storytelling is what the medium does best, and that it’s hardly ever used for that purpose.

Twelve-and-a-half years after it first began airing locally on Chicago’s WBEZ, This American Life remains a shining exception to that sad fact, with an estimated 1.7 million listeners tuning in to hear the show on one of the more than 500 public radio stations that carry it each weekend. The podcast that gets uploaded each Monday morning archiving the prior Friday’s This American Life broadcast is frequently the most popular one on the iTunes Music Store. (Though they're No. 2 this week, behind some Oprah thing. These Chicago media titans, honestly.).

But the most telling statistic is the fact that average listening time for the 59-minute show is 48 minutes. In other words, nearly everyone who turns on This American Life at any point during the broadcast listens all the way through to the end.

If Glass’s talk was about any one thing, it was about how Glass and his fellow writers and producers get those listeners to stay put. A clip from the show's classic "Cringe" episode illustrated his point that you can feel when a story is leading somewhere, and if the story is told in a certain way, our onboard software pretty much requires us to stick with it. Like a lot of great artists — and journalism, at the level at which Glass and his cohorts practice it, is an art — he’s completely forthcoming about his technique. Not every artist knows where his or her ideas and methods come from, of course. Glass’s, fortunately for us, arrived not from some mystical point of origin, but from years of plodding, painful trial-and-error.

After beginning as a National Public Radio intern 30 years ago, when he was 19, Glass worked in his 20s as a tape-cutter. (“I was never considered a contender” for an on-air gig, he recalled.) Certain passages of the recordings he was tasked with editing drew him in, and he tried to isolate the quality that made them so hard to ignore. Slowly it dawned on up that the sequences that held his attention all followed the same pattern:

Action — Action — Action — Moment of Reflection — Repeat.

Not until much later did he realize that his discovery was “like inventing a glass of water.” The fundamental structure of storytelling evolved in human beings more or less along with spoken language — he’d just taken the long way ‘round.

Glass’s aim, he said, when he began the show in late 1995 was to restore “human scale” — a phrase he used over and over again — to broadcast journalism, an alternative to “the fake, know-it-all gravitas” of most broadcast reporting, which "makes the world seem smaller and stupider and less than it really is.” Glass tried to dream up a show that would be analytical and smart as public radio must be, but that would hold the value of simple pleasure — fun — in equally high regard.

Indeed, that might be the single biggest reason that This American Life has more in common with the documentary films of Errol Morris or the writings of Studs Terkel (both oft-cited Glass influences) than with any network magazine news program: It follows its sources where they lead, instead of using people as props to support a premise that’s usually been decided upon before the actual reporting has even begun.

Pretty much any one of TAL's 353-and-counting episodes would work as proof, but Glass chose a few that were particularly unique: One was the story of Sam Slaven, a traumatized Iraq War vet suffering from bouts of rage whenever he found himself among Muslims back in the U.S. He set out -- in Glass's words -- "like a broken robot, to fix himself," joining a Muslim organization on his college campus to force himself to learn to live peacefully among them.

He also referenced one of TAL’s finest episodes, "Somewhere in the Arabian Sea,“ recorded aboard the aircraft carrier U.S.S. John C. Stennis in early 2002, shortly after the U.S. military had gone into Afghanistan to rout the Taliban. The show begins, memorably, with an interview with a 20-year-old female sailor whose job — 12 hours a day — is to refill the snack machines aboard a ship with a crew of more than 5,000.

“We’re a patriotic show, but we’re not corny about it,” Glass said, recalling that he and his staff were afraid of how their matter-of-fact account of day-to-day life on a warship would go over in the early months of the War on Terror. CNN and other news organizations were aboard the Stennis at the same time, and constantly putting their anchors on the flight deck to intone po-faced pablum about young men and women going “into harm’s way” — a phrase so pompous and overused that Bob Edwards actually banned it from the NPR airwaves.

Time and again, Glass recalled, he and his staff would ask crew members aboard the Stennis if they felt endangered. Most of them pointed out that they were aboard a floating fortress equipped with its own air force, protected by an escort of nuclear submarines and destroyers, in the middle of an ocean fighting an enemy that had neither warplanes nor warships. “It’s pretty safe,” they told him. “Back home in San Diego -- that’s dangerous.”

Before taking questions, Glass retold the Arabian Nights story of Scheherazade, the heroine who persuaded her murderous king to spare her life nightly for 1,000 nights by keeping him hooked on a very long story, until, on the 1,001st night her storytelling had engendered enough empathy within him to cure his need to kill. He likened this to a speech civil rights historian Taylor Branch had given in at the National Cathedral last month urging the two Americas simply to see each other. “That empathy is what makes us sane,” he said. “That empathy is what rescues us from Hell.”

That's a lot to ask of a story, maybe. Good thing we've got this guy on the case.

You can subscribe to receive This American Life as a free weekly podcast here. On Thursday, May 1st, TAL will conduct its first-ever live-video simulcast, an interactive program that will be shown in cinemas nationwide. You can find a participating theater and buy tickets here.