Last week Stitch Fix—the online personalized styling service—reported its quarterly earnings. Sales exceeded Wall Street’s expectations, but losses widened compared to a year earlier. The company also provided an outlook that suggested future growth would be difficult to come by. Shares plummeted accordingly. It’s yet another case of what I’ve come to call “profitless prosperity”—that is, retailers experiencing strong sales growth while actually turning a profit continues to be elusive.

This pattern of “disruptor brands” demonstrating often spectacular revenue growth is, by now, quite familiar. For more than a decade investors have plowed their money into digitally native vertical brands (DNVBs) and other (initially) online-only shopping platforms on the premise that sustainable companies could be built largely through leveraging a direct-to-consumer (DTC) business model. Underlying this investment thesis was that it was cheaper to build a brand online than through traditional asset-intensive retail models that required those pesky things called stores.

As more disruptors have IPO-ed recently (think Warby Parker and Allbirds) or, in Stitch Fix or Wayfair’s case, now have multiple years of being public, a disturbing pattern is emerging. Yes, these companies have innovated, often in dramatic ways. Yes, many have gone from being simple start-ups to businesses of significant scale, scope and complexity. Yes, quite a few have helped redefine customer expectations and challenged a status quo that desperately needed to be shaken up.

Yet, while many in the industry have already declared these brands to be successful, most continue to incinerate cash in rather spectacular fashion. And despite a perfect storm brought about by the Covid crisis, where a window of rapid acceleration to e-commerce and all things digital was handed to them, many high profile disruptor brands are seeing their losses grow, rather than finding a glide-path to profitability.

I’m confident that several of these companies will turn out to be sizable and sustainable over time. Yet it’s worth asking whether many of them are actually chasing markets that are much smaller than originally imagined and whether the underlying marginal economics of their business model can actually work. Without access to internal data and large scale consumer research, it’s impossible to be definitive on this point. But a few things are coming into sharper relief that investors would be wise to home in on.

First, the vast majority of these brands remain quite small and those that managed to surpass $100 million in revenues relatively quickly did so when targeted digital marketing costs were quite reasonable. Adding significant numbers of customers with positive customer lifetime value in the current environment is proving increasingly difficult, particularly with privacy policy changes.

Second, in the case of digitally-native vertical brands, many, if not most, are finding that a material physical store presence is required (through their own stores, wholesale distribution or a combination of both) to increase their total addressable market and, in theory, improve their profitability. While hundreds of stores have collectively been opened by these DNVB’s—with many more on the way—this strategy is far from proven. Among the publicly traded companies only Warby Parker is well into this strategy, with over 160 stores. But they too have seen their losses widening.

Third, it’s possible, if not likely, that out-sized growth is being propelled by unsustainable pricing and promotional strategies. At one level, it is admirable that Wayfair, Casper and others have reset the consumer expectations bar on what certain types of products should cost, thereby propelling their ability to steal share from industry incumbents. But I could sell a lot of $20 bills for only $15.

As someone who has been wondering aloud rather vociferously for years—here, in my book, in my keynotes, and on my podcast—about whether there might not be any “there there,”, I often get quite a lot of pushback.

Most of it is rooted in some form of “well, yeah, sure Steve, but X company lost a lot of money for many years and now they are killing it.” Often in this argument X = Amazon. But by now we all should understand that for Amazon, its first-party retail business has become a loss leader for its advertising and fulfillment businesses. When I ask for other examples, my antagonists usually point to other business models (Facebook, Uber, Airbnb) that have totally different operating dynamics.

The truth is the great acceleration of e-commerce has largely stalled and the marginal economics of online shopping (both in marketing and fulfillment) are increasingly challenging. This doesn’t mean it’s impossible for some disruptor brands to be successful over the long-term. But it does mean many will face stiff headwinds that will cause some to fail and others to massively restructure their growth plans.

A version of this story originally appeared on Forbes, where I am a senior retail contributor.