A girl smiles and waves jubilantly at the photographers. She’s 13 years old, with mousy hair tousled by the wind. With one hand she’s clinging onto the brick monument she’s just clambered up, her white pixie boots a little scuffed from the climb. In her other hand, she carefully clasps a packet of cheese and onion crisps. And she’s just saved the world.

In the springtime of 1987, the popular local newspaper, The Bedfordshire Times, splashed a photo of that grinning teenager across their centre pages. Usually their big story was of a cat rescued by firemen or the ribbon-cutting ceremony for a new shopping centre. But that week, the sleepy English town had been the focus of national interest. After years of political arguments, scientific controversies and local protests, a large nuclear waste company, ominously called Nirex, had announced they were cancelling plans to build a nuclear waste ‘deep storage facility’ in the town.

The local families who had fought so hard against the nuclear dump were taken by surprise. In a flurry of overnight activity, they built a small brick monument at the site where Nirex had been planning to store tonnes of radioactive waste. Then, as the photographers watched, the families began to accept their success and cry, hug and celebrate. The young girl in the photograph had been swept up in the emotion and scrambled up the bricks. No one really minded the scuffmarks or spilt crisps, because most of the people there also felt like climbing, shouting and punching the air. Small folk aren’t supposed to beat big corporations, and everyone was a little dazed.

I’m the girl. And thankfully my mum kept the news-clipping and had it framed for me. Today it hangs above my desk, and whenever I look up at it, I can vividly remember that moment. I was still a normal teenager, at least on the outside. But that photo captures the moment that my life changed. Because that was the first time I truly experienced how good it is to make a difference. Up on those bricks, with my dad’s steadying hand on my ankle, I felt like a superhero who had saved the world. Since that incredible flash of joy, I’ve had years to read a veritable mountain of books on the value of having ‘purpose’ in your life. Each of them analysing and trying to pin down that experience. Why does it feel so good to do good? Why do so many successful people leave high-flying careers to pursue purposeful work that helps others? I believe most of the books miss an important feedback loop in making a difference. They assume that ‘purpose’ is almost an indulgence, or a spiritual need. But in a world which feels totally overwhelming, where fear and worry can leave even the most successful people sleepless and anxious - taking positive action builds a sense of control. And that sense of impact and ‘rightness’ has a tangible physical and emotional value. In a world of fear, being a hero can save your life.