It’s hard to think of a better recent success story in Silicon Valley than Uber. The ride-hailing company, valued by investors at $51 billion, isn’t quite six years old yet, but it has already expanded aggressively, setting up operations in 400 cities across six continents and offering new features like courier and food-delivery services. It’s cleared regulatory hurdles and dealt with hostility from entrenched, sometimes powerful local transportation interests. Though it’s losing money as it grows, the argument goes, what hyper-growth-stage tech company isn’t? Amazon went public while it was still in the red, and now it’s arguably the top player in the e-commerce business.

Given its ubiquity and success, it seems natural that Uber has spawned a series of look-alike on-demand companies. Some, like Postmates, deliver your lunch in less time than it would take to walk to the chopped-salad place across the street; others, like Luxe, park your car for you on-demand. Just as quickly as the Uber-for-X market blossomed, it became an in-joke: suddenly, there was an Uber-like service for everything. As Aziz Shamim once overheard: “SF tech culture is focused on solving one problem: What is my mother no longer doing for me?”

Unlike Uber, however, a lot of these companies are not universally finding success. Many initially had unsustainable business models, offering low prices for users subsidized by their venture-capital funding. Now, prices are going up as companies realize that capital is a finite resource and the unit economics of their businesses are not sustainable. In fact, some of them have folded entirely or shifted away from the on-demand model. DoorDash recently closed a $127 million mega-round—an increasing rarity in Silicon Valley’s current, chilly funding climate—but it did so in a “down” round, meaning that investors believe it is worth less today than it was before.

The New York Times’ Farhad Manjoo calls this era “the end of the on-demand dream” in an article published Wednesday. “The initial phase of hype and euphoria is properly over and the shake-out has already begun,” one Edison Investment Research analyst recently concluded. “Only the strongest with the most money are likely to survive and will do so by buying up the competition or waiting for them to wither on their own. For the rest, the unicorn disguises are already slipping revealing the true colors of the donkeys underneath.”

Some of the start-ups hoping to avoid that fate have found success in vertical integration, like online clothes retailer Everlane and razor company Harry’s, which control their entire supply chains. Bigger players like Amazon are moving to cut out the delivery middlemen, too, trying to own the entire end-to-end logistics experience by experimenting with drone delivery and their own leased planes. As it expands its logistics capabilities, Uber has the potential to swallow smaller players across different delivery markets, including Caviar, a food-delivery service acquired by Jack Dorsey’s payments company Square.

Silicon Valley’s tech bubble has begun to contract. There have been layoffs, shuttered companies, dwindling funding for V.C.-backed start-ups, and a sobering realization among founders that they need to push for profitability to survive. Even tech employees are getting jittery. Like any market, the on-demand economy will have its share of both massive successes and huge failures alike. But when the bubble bursts—whether it’s a slow leak of hot air over many years or a sudden explosion—only the more prudent companies will be left standing.