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We are all crying, or we soon will be. New Yorkers, faced with the near-certainty of home isolation for weeks or months to come, can’t believe — can’t accept — that the mighty metropolis has been laid low by an enemy too small to be seen.

Today’s mood is different from what it was after 9/11 — not defiant but funereal. To save our city for the inevitable day when the virus is routed, we need to quit whining and get on with the lonely but indispensable task ahead of us.

With apologies to Don Corleone’s face-slap to simpering Johnny Fontaine, we can again act like the brave city we claim to be. But it calls for a different brand of internal fortitude than the one that saw us through previous crises.

The scourge of the coronavirus strikes many of us as something supernatural. Resignation and fatalism are in the air. Despair unrelieved by even glimmers of hope befouls social media and traditional media alike.

To those who say we can’t go on like this, my friends, we must. And we will, however agonizing a remove from the daily outside routines that define our lives might be.

It’s in the nature of nightmares and waking crises for each to be different. Sandy wasn’t the same as the Wall Street crash, which wasn’t the same as 9/11, which wasn’t the same as Pearl Harbor when our young men faced death thousands of miles away and their loved ones wondered if they’d ever come home.

This time, adrenaline won’t help. The energy surge to kick the bug’s butt will bring on precisely the ­let’s-lock-arms behavior that will only accelerate its spread.

We need to accept the reality of prolonged entrapment in our homes, removed from the therapeutic stress of work and the pleasure of play. The challenge is the same whether we dwell in a Park Avenue penthouse or in a sunless basement in Queens.

It will strain marriages, friendships and our sanity. We normally in-your-face New Yorkers must cope with our own frightened faces in the mirror.

But this is our duty. If we do what we now must, we will one day build a new city on the ruins. And we will rise to the occasion, however lonely it might be.