This October, amid a spate of good news, investors bid the shares of electric-vehicle pioneer Tesla up into the stratosphere, making it one of just a handful of American companies to be worth more than $1 trillion in market capitalization. As of market close on Nov. 29, Elon Musk's auto-industry upstart was worth $1.14 trillion. That puts it alongside four other current members of the Trillion Dollar Club—Amazon, Microsoft, Apple, and Alphabet—each of which has many, many times more revenue than Tesla.

Tesla's $1 trillion-plus valuation in part reflects faith and buzz, and the widespread belief that the company's innovative technology and its maverick CEO will rank it among the titans for decades to come. But as Fortune is reporting this week, it also reflects more specific assumptions about what benchmarks Tesla will hit as an actual business—and those assumptions should give shareholders cause to be nervous.

As David Trainer, founder and CEO of research firm New Constructs, pointed out in a recent report, Tesla’s market value now exceeds the total value of the world’s 10 largest automakers by market cap, a group that includes Toyota, General Motors, Ford, and Daimler, home of Mercedes. Those top 10 sold 45 million cars in their past four quarters—more than 50 times as many as Tesla sold.

That crazy imbalance reflects the enormously high value investors are giving to Tesla's stock—more than 350 times earnings, as of mid-November—and the puny valuation they're giving to all the other automakers (about 7.4 times earnings, by Fortune's calculations).

And what that means is sobering: To buy Tesla’s shares today, at current prices, is to make the ultimate long-shot bet. Investors are wagering that Tesla will mine massive profits in electric cars while its competitors—all of them, with all their technical expertise and person-power—will flop en masse. Put simply, investors are saying that Tesla will sweep the field and leave others to fight over the scraps.

Is it possible? Of course. Is it likely? Not very.

A version of this article appears in the December 2021/January 2022 issue of Fortune.