Feldman's foray into the field of forgiveness began when she interviewed Azim Khamisa - an international investment banker, whose only son, Tariq, a 20-year-old student at San Diego State University, was shot dead in 1995 while delivering pizza. The bullet had been fired by 14-year-old Tony Hicks, as part of a gang initiation, "Jacking the Pizza Man". Despite his grief, Azim reached an extraordinary conclusion: "There were victims on both ends of the gun. I chose to forgive 20 years ago, and it has brought me to peace."
"As a grudge-holder by nature, I was fascinated," says Feldman. "Azim had forgiven his son's killer, and not only forgiven him, but reached out to the killer's family and became close friends with them - together they started an organisation devoted to violence prevention work with at-risk youth."
What began as a straightforward interview turned into a two-year investigation into the F-word. Her book grapples with what forgiveness means in the first place, why it matters, and how you go about mustering up compassion for someone who has wronged you - or yourself for the mistakes you've made in life.
In Azim's case, not everyone understood his decision to forgive, including Jennifer, Tariq's 20-year-old fiancee of just six weeks. "Jennifer was never able to forgive, although I worked with her for many years on this," says Azim, sadly. Seven years after Tariq died, Jennifer overdosed and committed suicide.
"One point that's important is how misunderstood forgiveness is," says Feldman. "I had always associated forgiveness with condoning or excusing a behaviour; if you forgave something then you couldn't seek justice, or file charges, or sue. That's not the case. Just because you forgive, it doesn't mean you have to excuse. I'm not saying we can't be angry. Anger is a natural response to pain and injustice. Anger motivates action. It's when anger hardens into bitterness and resentment that it becomes dangerous."
Feldman's quest to understand the nature of forgiveness took her as far as Rwanda, to hear the stories of genocide survivors, but she also found a lot of material much closer to home - people who were bullied at school, betrayed spouses, neglected children who forgave their parents.
The implications of forgiveness seem enormous. It has been much maligned for years, dismissed as religious dogma, or as weak, letting criminals off the hook, and even disrespectful to victims. "But the Merriam-Webster [dictionary] definition of 'forgiveness' is 'to give up resentment'," points out Feldman. "Giving up resentment doesn't mean excusing. It doesn't mean relinquishing justice, and it doesn't require reconciliation."
After she'd established what forgiveness meant to her, Feldman turned her attention to its effects, and swiftly found herself assessing 20 years' worth of research into its psychological and physiological benefits. She quotes Dr Frederic Luskin, co-founder of the Stanford Forgiveness Project at Stanford University, who explains: "When you don't forgive you release all the chemicals of the stress response. Each time you react, adrenaline, cortisol, and norepinephrine enter the body. When it's a chronic grudge, you could think about it 20 times a day, and those chemicals limit creativity, they limit problem-solving. Cortisol and norepinephrine cause your brain to enter what we call 'the no-thinking zone,' and over time, they lead you to feel helpless and like a victim. When you forgive, you wipe all of that clean."
When he talks about forgiving Hicks, Azim quotes Mandela: "Resentment is like drinking poison and then hoping it will kill your enemies." As Feldman points out: "It turns out this is literally true - harbouring resentment increases your risk of heart disease over time. Resentment damages your brain."
However compelling the psychological and health benefits may seem, the question of how to put theory into practice remains. But Feldman is adamant that it can be harnessed through exercises that foster compassion and empathy, much like CBT rewires the brain.
There are huge social gains to be made by embracing forgiveness, and Feldman argues that it warrants serious consideration within our social institutions, citing school and juvenile justice programmes which have implemented "restorative practices" - based on reaching resolution between victims and offenders - not just in the US, but closer to home, in Hull.
Indeed, The Hull Centre for Restorative Practices, founded in 2007 by John Macdonald and his wife Estelle, began implementing such practices among the city's public services after Mrs Macdonald, also head teacher at Collingwood Primary School, used them to take her school from special measures to outstanding. Under her headship not a single child has been excluded in the past 10 years and Collingwood is now one of a network of 10 "restorative" schools across the city. Similarly, Humberside Police now use restorative practices to deal with all first-time offenders, which has halved reoffending rates among young criminals.
Today Azim is a speaker, author of three books on forgiveness, and chief executive and founder of the Tariq Khamisa Foundation which tackles youth violence. In two weeks he's running a two-day forgiveness workshop in Surrey as part of theforgivenessproject.com.
He's the leading light in the forgiveness field, which was empty in 1998, when he wrote his first book. "Back then, for any reflection on forgiveness, you had to look to the scriptures," he says. "Today it's a widely respected field with a huge body of scientific research to back it up."
"When I stopped blaming the world, it changed my life," concludes Feldman. "Forgiveness isn't about the past, it's about the future. And it's not just about forgiving others, but about forgiving yourself. Don't beat yourself up for that mistake you made a year ago - or this morning."
Additional reporting: Joe Shute
