One common piece of investing advice is the adage that companies should ‘under promise and over deliver’ to keep share prices chugging higher. The alternative of delivering results below expectations can be the death knell, especially for new businesses trying to disrupt or create entire new industries.

So, it’s interesting to note that technology companies which already carry high valuations that imply high expectations seem to take the opposite tack, and promise to change the world on a regular basis.

Whether its in robotics, which even Elon Musk recently acknowledged, “Excessive automation at Tesla was a mistake. To be precise, my mistake. Humans are underrated,”  or in artificial intelligence, which Mark Zuckerberg admitted failed and will be incapable of detecting “fake news,” to say nothing of UBER’s misleading progress regarding self-driving cars, the full promise of technology not only seems still far in the future, but might ultimately never deliver on its potential.

But at the moment, investors still seem enthralled with tech stocks, especially the large cap, winner take all of the FANG stocks of Amazon, Facebook, Google etc.

This group not only represents a whopping 34% of the Nasdaq 100 and a full 19% of S&P 500, but is currently the most over owned group by mutual and hedge funds around the world. 

This could setting the group up for massive disappointment in coming years.

From historically elevated P/E ratios and a rash of global scandals to escalating regulatory concern about tech giant monopolies, there has been constant evidence over the past year that tech’s market leadership is more fragile than it seems. Yet, time and again, tech companies and venture capitalists have renewed euphoria by selling the technologies of the future as imminent panaceas for the technology-driven problems of the present.

Long term, there is little doubting the disruptive potential of emerging technologies, whether it’s robotics, machine learning, or blockchain. However, as Musk’s admission illuminates, the near-term promise of these technologies to generate real-world value has likely been oversold. Hand-in-hand with an E.U. and U.S. regulatory backlash, a seismic sentiment shift toward the technologies of the future could catalyze an equity downturn with contagion implications across the economy.

 Related: Are the Markets Rigged? The SEC Investigates.