Note: This piece contains vague spoilers for the middle act of “Portal 2.” There’s nothing earth-shattering, but if you’re one of those people who regards every little disclosure as a game-ruining experience, please come back again soon.

As I played through “Portal 2” [review], I found myself caught up in its middle act, in which Valve relates the story of Aperture Science, founder Cave Johnson and GLaDOS, the maniacal artificial intelligence who runs Aperture now that most of the humans who worked there are dead.

It’s a captivating, hilarious and slightly heartbreaking story, as well as a cautionary tale about opportunists’ tendency to prey on society’s least fortunate. And it’s told mostly through audio diaries.

You know audio diaries, those little recordings that have become almost ubiquitous in action-oriented video games that aim to tell a serious story. In the two “BioShock” games, they were indispensable collectibles that explored the history and social tensions in the ruined underwater utopia of Rapture. In “Dead Space,” they filled Isaac Clarke and players in on the tragic events that transpired on the USG Ishimura, and their use carried over to “Dead Space 2.”

In “Portal 2,” the audio diaries aren’t collectible. They merely play when you reach certain points in the levels. They range from informative to entertaining. (My favorite involves a group of test subjects who volunteered to be injected with mantis DNA being told instead that the experiment has been canceled, and that they’ll now need to help fight “an army of mantis men.”)

Even though I’m not sure I’d have “Portal 2” or the “BioShocks'” stories told any other way, the games’ frequent use of audio diaries got me thinking: Has anyone ever actually kept an audio diary? Has anyone you know walked around with a tape recorder to capture their thoughts?

President Richard M. Nixon may have been the closest thing to a prolific audio diarist our society has ever known, but the guy recorded everything. It kind of makes you wonder whether there are secret Andrew Ryan or Cave Johnson tapes lying around, where they tell their assistants what to pick up from the store, or remind themselves of important appointments.

Even though they’re fairly unrealistic, audio diaries will be in games for years to come because gamers hate reading, or at least developers think we do. Meanwhile, designers of action-oriented games cling to them because they can relay expository information without pulling players out of the moment and forcing them to read a bunch of stuff or watch little movies.

Still, you have to wonder if some up-and-coming game designer will figure out a better way to relay expository information in a way that doesn’t require us to believe that everyone stands around and records their innermost thoughts on a little handheld recorder, then leaves the tapes lying all over the place for humanity’s last, best hope to find.