It usually goes along success stories, and though in some cases it can be less shameful and more positive, such as a shortcut for better results, more often it refers to a blemish in that success story not yet public.
For instance, in the Freakonomics post “The Quarterback Quandary”, Stephen Dubner says:
It’s not fair to say that the NFL draft is a total crapshoot. First-round players generally perform better than second-round players, who generally perform better than third-rounders and so on.Early this year there was an interesting The New York Times article called The Dirty Little Secrets of Search, about the surprising appearance of certain companies' names on top of Google searches not so clearly related to the companies activities:
But there’s a dirty little secret that most people won’t acknowledge, or don’t even recognize. Selecting a player in the draft is essentially trying to predict the future, and human beings are simply not very good at it.
The New York Times asked an expert in online search, Doug Pierce of Blue Fountain Media in New York, to study this question, as well as Penney’s astoundingly strong search-term performance in recent months. What he found suggests that the digital age’s most mundane act, the Google search, often represents layer upon layer of intrigue. And the intrigue starts in the sprawling, subterranean world of “black hat” optimization, the dark art of raising the profile of a Web site with methods that Google considers tantamount to cheating.So the dirty little secret is that those companies were manipulating Google to show their names in a prevalent position.
And, finally, I found an even simpler example, in one of Scott Bourne's Photofocus post "Seven Ways To Reduce Sensor Dust". It starts:
It’s the dirty little secret of digital photography. Dust on the sensor.This is a pretty clear example: the caveat they didn't warn you about when you bought your camera.
Do you want to learn more dirty little secrets? Just follow this link.