The "September 11 effect" is the popular label given to New York's sense of community after the 2001 attacks, as the city coped with the largest power outage in US history.
"After September 11, we became a community rather than just a collection of individuals," explained 28-year-old New Yorker Matt Mulroy.
Riots and looting marked the previous citywide blackout in 1977. But the crisis that ended on Saturday was notable for the many simple acts of kindness and generosity it inspired.
New Yorkers shared drinking water, food, cars and even their homes with tens of thousands of stranded commuters with no way home and no place to sleep.
Financial journalist Ciara Linnane, who managed to escape her office in the World Trade Centre when the twin towers collapsed in 2001, was riding in a taxi when the blackout struck Thursday afternoon.
Fears of another attack popped in Linnane's mind as she saw traffic signals black out and subway riders streaming out of stations.
"My first thought was just 'oh my God', but then I heard the explanation on the cab radio," said Linnane. Her second thought was to tell the driver to pick up two pregnant women standing at a bus stop.
"September 11 definitely changed something," Linnane said.
"After September 11, we became a community rather than just a collection of individuals"
New Yorker Matt Mulroy
"New York used to be a more aggressive city, but now when something happens like this, you see people helping each other out, talking to each other in the street and in the bus.
"You even get a sort of party mood. In my neighbourhood, people were letting off fireworks when the lights came on again," Linnane said.
And the New York police also played their part. Given the length of the blackout, there was little crime, which Police Commissioner Ray Kelly attributed in part to a rapid deployment of officers, especially in high-risk areas.
The quick response was shaped by repeated counter-attack exercises the police have carried out over the past two years.
Some 10,000 police officers were put on street patrol, while special units were deployed at sensitive locations, such as bridges and hospitals.