Politicians and police are actively encouraging us to intervene if we witness violence on the street.
But why do some of us become natural 'have a go heroes' in these situations, while others chose to 'walk on by'?
In an attempt to find out, Nick Ross meets the people studying the psychology of how we respond when we witness violent behaviour.
His investigation uncovers surprising CCTV evidence that people are actually much more likely to intervene than previously suspected.
And he takes part in virtual reality experiments in which people's responses to emerging violence are tested using life-size and frighteningly realistic avatars.
The 'bystander effect', he learns, suggests that the more people who witness a violent event, the less likely it is that any individual will intervene.
And this phenomenon turns out to be equally true in cyberspace.
Producer: Brian King
An Above The Title production for BBC Radio 4.