Anniversary No. 1: Exactly four years ago, Lehman Brothers filed for bankruptcy protection. In the days and weeks that followed, we saw the unfolding of the dramatic — and ultimately successful — effort by the federal government to rescue the banking system. But, once the dust settled, we began to see something else: like the stock market crash of 1929, Lehman wasn’t an isolated event. Rather, it was a signal that deep problems had enveloped our economy — problems that wouldn’t be solved quickly or easily. That is why the Lehman bankruptcy still resonates. It was the moment everything changed.

Prior to Lehman, it was easy to believe that housing prices could only go up and that we could always rely on debt to maintain our standard of living. We shrugged as manufacturing jobs disappeared — 5.8 million just since 2000 — and good middle-class jobs became harder to find. We didn’t talk much about income inequality. Nor did we care much that Wall Street had developed a mercenary trading culture, which had little to do with providing capital for companies, ostensibly its reason for being.

Post-Lehman, economic reality set in. First came the Great Recession, followed by a recovery so weak that unemployment remains at around 8 percent. The huge debt overhang is a yoke holding back economic growth. Millions of homes have been foreclosed on. The Federal Reserve has continually opened its monetary spigots to boost the economy — as it did again this week — but the problems are simply too big to be fixed by monetary policy alone. That’s the world we live in now.

Inevitably, this sense of never-ending economic struggle has led to a great deal of anger. On the right, that anger found its voice in the Tea Party. Its core belief is that government is the enemy, and that a more hardhearted approach — slashing government spending and forcing people to fend for themselves — is the best way to get back on track. However misguided, its conviction cannot be doubted.

On the left, that anger led, a year ago, to the rise of the Occupy Wall Street movement. Thus, Anniversary No. 2: Sept. 17, 2011, was the date Occupy Wall Street took over Zuccotti Park in Lower Manhattan, which soon led to similar actions in cities across the country. The movement’s primary issue was income inequality — “We are the 99 percent,” they used to chant. Reporters swarmed into the park, interviewing Occupy protesters and speculating on whether Occupy had the potential to be a lasting force. “Can Occupy Wall Street Become the Liberal Tea Party?” asked The American Prospect magazine.

A year later, we know the answer: It can’t, and it isn’t. For all intents and purposes, the Occupy movement is dead, even as the Tea Party lives on. But why?

One reason, it seems to me, is that the Occupy protesters were purposely — even proudly — rudderless, eschewing leadership in favor of broad, and thus vague, consensus. It’s hard to get anything done without leaders. A second is that while they had plenty of grievances, aimed mainly at the “oppressive” power of corporations, the Occupy protesters never got beyond their own slogans.

But the main reason is that, ultimately, Occupy Wall Street simply would not engage with the larger world. Believing that both politicians and corporations were corrupt, it declined to dirty its hands by talking to anyone in power. The takeover of the park — especially as the police threatened to force the protesters out — became an end in itself rather than the means to something larger. Occupy was an insular movement, whose members spoke mainly to each other.

The Tea Party did just the opposite. It, too, believed that politicians were venal, but rather than turning away from politics, its adherents worked to elect politicians who believed in the same things they did. Yes, the Tea Party had wealthy benefactors, but their money would not have succeeded without enormous grass-roots support. Two years ago, 87 new Tea Party-elected candidates showed up in Washington. Much as you or I may not like it, they have largely succeeded throwing sand in the wheels of government. That was their goal.

Timothy Noah, the author of “The Great Divergence,” a fine book about income inequality, says that Occupy Wall Street did succeed in “massively raising the issue’s profile,” as he put it to me in an e-mail. There is more discussion now about income inequality, he added, than during the entire quarter-century the income gap was widening.

That is nothing to sneeze at, I suppose, but raising the issue is the easy part. The hard part is doing something about it. Without political engagement by those who want to reverse income inequality, it will continue to widen.

Occupy Wall Street gave us a memorable slogan — “the 99 percent.” But you know what they say. Talk is cheap.