Before it fueled the run-up in GameStop’s stock, WallStreetBets, the Reddit message board, had another claim to fame: It helped popularize a series of memes centered on the Federal Reserve chair, Jerome H. Powell, and his central bank’s policy of keeping interest rates near rock bottom while buying government bonds to bolster the economy.

“Money printer go brrrrr,” many of them read, suggesting that the Fed chair was essentially printing money and propping up markets by pumping cash into them through its program to buy government-backed bonds.

Reddit and Twitter made images playing on Mr. Powell’s persona — he’s referred to almost exclusively as “JPOW” on WallStreetBets — so ubiquitous that they’ve become paraphernalia. Amazon now sells sweatshirts (Prime eligible!) printed with an image of the Fed chair as a Christ figure ringed in a halo of golden light. In place of the Bible, the gospel he holds declares, “Recession canceled, stocks only go up.”

The blind optimism embodied in that statement — one might call it irrational exuberance — runs the risk of inflating bubbles in markets. Some experts see the saga of GameStop as a cautionary example of problems that can develop when investors get swept up in market momentum, driven to some extent by the Fed’s attempts to keep the economy humming along with low rates and bond purchases.

“We’re observing a market mania, and the cost of money has something to do with this,” said Peter Fisher, who teaches finance at Dartmouth’s Tuck School of Business and once served in the Treasury Department and Federal Reserve. “It’s just not credible to suggest that the momentum in equity markets has nothing to do with the Fed’s efforts to keep interest rates so low for so long.”

To be clear, GameStop has been an unusual situation.

Hedge funds had been betting against the retailer’s stock, or “shorting” it, assuming its share price would fall. A rush of retail traders coordinated to make that bet go bad by pushing up GameStop’s price. Because of the way short selling works, the hedge funds were forced to buy GameStop themselves to limit their losses. The stock price skyrocketed, jumping more than 600 percent in days.

A mass of newly minted retail investors has poured into the stock market over the last year, thanks to a confluence of factors including fewer social opportunities and work-from-home arrangements, temporary disruption of sports betting and the rise of trading that is billed as “commission free.” Retail trading of individual stocks now represents roughly 25 percent of overall stock market volume compared with just 10 percent in 2019, according to Goldman Sachs.

But a shared belief that this is a good time to buy stocks is also fueling that trend.

Leaving aside the surge — and then the crash — in so-called meme stocks, the market appears to be flirting with euphoria. Price-to-earnings ratios and other market barometers are at heights not seen in two decades, since the tail end of the dot-com boom.

Much as they did in the tech stock frenzy of the 1990s, individuals are pushing levels of trading activity sharply higher, traders are borrowing on margin to buy stock, and investors are snapping up public offerings from unprofitable or unproven companies.

Analysts across Wall Street say the traditional drivers of stock price movements — changing expectations for corporate profits and revenues — have in many cases become less relevant.

In fact, the surge has come when the American economy remains damaged by the coronavirus pandemic. Fresh data released on Friday showed the economy in January was still nearly 10 million jobs short of employment levels that prevailed before the virus struck.

Some of the bump has come because investors are placing their bets based on expectations about corporate prospects once demand has snapped back and the job market has healed. But analysts said a combination of fiscal stimulus — including checks that put money into consumers’ pockets — and the Fed’s cheap money policies have also helped bolster stock prices.

The timing checks out. When the Covid-19 crisis first gripped the United States last February and March, the market plunged. The S&P 500 — which had been at record highs — collapsed by nearly 34 percent in a matter of weeks. Conditions became so volatile that even typically stable markets, such as that for Treasury bonds, began to malfunction under the strain.

To keep the panic from freezing the financial system and worsening the economic damage, the Fed cut interest rates nearly to zero on March 15 and announced a series of major actions on March 23. The central bank said that it was willing to buy unlimited quantities of government-backed debt, and that it would tiptoe into the corporate bond market for the first time ever to prevent the pandemic’s market fallout from turning into a full-blown financial crisis.

Markets rejoiced. Stocks bottomed out and then ricocheted higher, climbing a 9.4 percent the next day and ultimately staging the best three-day performance for the index since 1933.

“When essentially your central bank has drawn a line in the sand, as they did last March, then people understand that it’s a one-way bet,” said Paul McCulley, former chief economist of Pimco, a giant asset management shop.

The S&P 500 stock index has jumped more than 70 percent since then. To put the breakneck speed of that run-up into context, the S&P 500 has climbed about as much over the past 10 months than it had in the four years leading up to the pandemic.

When it comes to the Fed’s influence on stock prices, some of it is purely mechanical. When companies can borrow for less, it allows for bigger profits and cheaper business expansion opportunities, which could elevate their worth in the eyes of stockholders. Some of the increase probably reflects the reality that super-low rates push investors out of bonds and into riskier assets like stocks as they seek better returns.

But analysts warn that part of the run-up simply owes to sentiment: Investors believe stocks will go up, in some cases because they believe in the Fed, and so they keep buying.

The downside is that people can lose faith in an ever-rising stock market. And when the music stops, an optimism-fueled bubble can become a pessimism-pricked burst.

GameStop in particular “does illustrate some of the financial vulnerabilities that can stem from ultra-loose monetary and fiscal policies,” Neil Shearing at Capital Economics wrote in a research note last week, noting that super-low interest rates, government stimulus payments, lockdowns and platforms that democratize trading have all come against a backdrop of “longstanding societal strains and the perception of a widening schism between Wall Street and Main Street.”

Still, Mr. Shearing said in an interview, the stock market as a whole does not yet look dramatically overextended, and the Fed needs to focus on righting a pandemic-damaged economy — which is the goal of its low-rate and bond buying policies.

The Fed argues that it is not driving asset prices to the degree that many believe. While Mr. Powell, the Fed chair, declined to discuss GameStop specifically at a news conference in late January, he painted financial risks over all as “moderate.”

“If you look at where it’s really been driving asset prices, really in the last couple of months, it isn’t monetary policy: It’s been expectations about vaccines, and it’s also fiscal policy,” Mr. Powell said. “I think that the connection between low interest rates and asset values is probably something that’s not as tight as people think because a lot of different factors are driving asset prices at any given time.”

But if, as many believe, the Fed’s low rates are a substantial part of the story, it’s unclear that raising them slightly would stop a run-up in stock prices. While slowing bond purchases probably could take the shine off investors’ enthusiasm, that could come at a cost to the real economy.

Regardless, Fed officials are unlikely to try to cool things off in the market any time soon.

“If one group of speculators wants to have a battle of wills with another group of speculators over an individual stock, God bless them,” Neel Kashkari, the Minneapolis Fed president, said at a virtual town hall event last week. He added that he was not “at all thinking about modifying my views on monetary policy because of speculators in these individual stocks.”