The Federal Reserve says the timing of its first interest rate hike in nine years depends on the data, but that doesn’t mean the Fed will be digging through the jobs, growth and inflation reports for the all-clear signal.

Instead, the Fed will be doing what millions of people have been doing for the past couple of weeks: Watching the stock market.

Many investors have assumed that the recent selloffs in markets from Shanghai to New York meant that the Fed definitely won’t pull the trigger on a rate hike at its Sept. 16-17 meeting. Many prominent talking heads – from Suze Orman to Jim Cramer – are explicitly begging the Fed to hold off on higher interest rates as a way to protect stock prices.

It seems they still fervently believe in the “Greenspan put.” They assume that the Fed will always come riding to the rescue of the markets, as Fed Chair Alan Greenspan did so many times.

You can’t blame them for believing that, because from 1987 to today, the Fed has reacted to nearly every market hiccough and tantrum by flooding markets with liquidity and reassurances. They’ve given the markets rate cuts, quantitative easing and promises that easy-money policies will continue for a long time, if not forever.

This “Greenspan put” means investing in the stock market is a one-way bet.

On Wednesday, New York Fed President Bill Dudley seemed to close the door on a September rate hike when he said that, “at this moment,” a rate hike next month no longer seemed as “compelling” as it once did. Traders in federal funds futures lowered the odds of an increase in September to about 24%, down from about 50% just before the global market selloff intensified last week.

But Dudley didn’t take September off the table, as many people have assumed. Indeed, he explicitly said that a September rate hike “could become more compelling by the time of the meeting as we get additional information.”

And what sort of additional information would make a rate hike more compelling? Dudley said the Fed is looking at more than the economic data, widening its scope to examine everything that might impact the economic outlook. They are looking at the value of the dollar, the price of commodities, the risk of contagion from Europe, from China, and from emerging markets. And, above all, the U.S. stock market.

I believe the market selloff has made a September rate hike even more compelling than it was before, because it gives Fed Chair Janet Yellen the opportunity she needs to kill the “Greenspan put” once and for all.

Fed officials really, really want to raise interest rates, not because they think the economy is completely healed from the Great Recession, and not because they think too many people have jobs, and certainly not because they fear that inflation will suddenly come roaring back.

They know there are still too many people out of work, and they know deflationary pressures are strong. But they think they’ve seen enough progress on moving toward their dual mandate of full employment and stable prices to begin the process of normalizing interest rates.

Also read: Fed will raise rates in September

There’s only one thing holding them back: Financial instability.

Even dovish Fed policy makers such as Dudley think a rate hike now is “compelling” because they worry that extraordinarily low interest rates for an extremely long time breed complacency in business leaders, investors and consumers. They worry about fueling financial instability, as the Fed tragically did in the late 1990s and again in 2005 and 2006.

In short, they want to raise rates to kill the “Greenspan put.”

Also read: Yellen should take away the punch bowl

Officials have been obliquely warning that some stock market valuations are too high to be justified by fundamentals. In truth, the correction in the U.S. markets has been welcomed at the Marriner Eccles Building. The Fed doesn’t mind the dip in the Dow, because it punishes complacency and because the selloff has been relatively orderly. There’s been no panic on Wall Street.

Also read: Why a stock-market selloff won’t crash the economy

If markets remain orderly between now and Sept. 17, there’s a good chance the Fed will raise the federal funds target rate by a quarter point. But if the selloff continues, or if it seems to be spooking corporate leaders into delaying or postponing their expansion plans or making consumers re-examine their spending plans, then the Fed will probably delay its rate hike as well.

Fed officials have done a terrible job of communicating their policy to the public, which is why so many believe in the “Greenspan put.”

The point of easy monetary policy isn’t to goose the stock market as an end unto itself. The Fed’s goal is get the economy moving on its own again, and to do that investors and businesses need to abandon caution and embrace risk. The Fed wants businesses to invest in the future, which means investors need to put their money into productive investments instead of riskless Treasurys.

But if supposedly risky investments like corporate equities and bonds are actually guaranteed by the Fed’s “Greenspan put,” then investors aren’t embracing risk at all.

The good news for the Fed is that companies are embracing risk as the economy continues to heal. The business sector (excluding the oil extraction industry) is putting money to work again, building factories and shops, buying equipment, and ploughing funds into research and development.

If businesses keep doing that, the economy and the markets will do fine.