Why many people don’t help when encountering someone in distress?

Two people who prevented a woman from jumping off a bridge in St. John, N.B., are wondering why other motorists on the bridge wouldn't help them keep the dangling woman from falling.

CBC News reported Jane Foster and Kurt Delaney held onto the woman after she stepped off the Reversing Falls Bridge this week.

"I could see people in their passenger seats just kind of looking at us," Foster told CBC News. "I was wishing for at least one more person, because the two of us — I don't think we could have held her."

Foster arrived on the scene first and tried to talk the woman into climbing back over to the safe side of the railing, urging another motorists to call 911. Delaney ran to help after witnessing the drama from a nearby street.

"Everything pretty much played through my mind," he said. "I thought to myself, I'm probably doing what everyone else is doing: sitting here and contemplating all these different things when really I should go and see what's going on."

The two each managed to grab an arm, which was fortunate because as the woman heard approaching sirens she announced "I'm going to go," and stepped off, Delaney told CBC News.

Foster lost her grip on the woman's arm, leaving Delaney bent double to hang on to her until police arrived to help haul her in. None of the other motorists came to help.

"I just don't understand," he said. "If you see someone hanging from a bridge like that, you need to act. Every second counts."

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There's actually a name for this phenomenon. It's called the bystander effect. Studies have found the more people who witness someone in distress, the less likely they are to help. People are more inclined to intervene if they are alone or with just a few others present.

Perhaps the most famous modern example was the 1964 murder of Kitty Genovese, who was raped and stabbed to death in New York City. The attacks — her killer left, then returned minutes later and renewed the assault — and her screams for help were ignored by at least a dozen people in neighbouring apartments. The killing prompted a wave of soul-searching about the callousness of modern society and launched research into the bystander effect.

With the advent of security video, we've seen other examples firsthand , like the 2011 case of a a two-year-old Chinese girl who wandered into traffic and was run over twice as passersby ignored her for seven minutes.

In a 2007 incident in Detroit, a 91-year-old war veteran was beaten and carjacked as bystanders just metres away ignored the assault, ABC News reported.

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And earlier this year, a man was beaten and stabbed inside a Detroit gas station convenience store while other customers watched.

And, of course, the advent of smart-phone video has turned us into voyeurs instead of helpers, such as this case of a beating in a Baltimore fast-food outlet, where staff and customers did nothing as the victim was pummelled. A lone woman tried to help.

Our reactions to a crisis are complex. Sometimes we find it hard to believe what we're witnessing is real; we see so much realistic-looking drama on TV. It sometimes takes a conscious effort, as Delaney said, to decide to help.