I studied economics because I was good at it. But when I started university in 1969, the time of revolutions, everybody wanted to make a difference. Economics didn't seem to fit. A professor told me to stick with it and take a Masters in international development, as that was where economics really meant something. It was a determining moment in my life. I was considering a switch to international relations, and may have ended up in academia or the Foreign Office.
My first job was in the public affairs unit of Oxfam. They sent me to New York, saying 'go and lobby the UN about Cambodia'. I influenced a resolution, and that year the country got £20m of aid that it wouldn't have otherwise. It taught me what you can achieve if you're in the right place at the right time and you believe you can do it.
At 33, I became chief exec of an environmental NGO in Nairobi. I flew off with my wife and six-month-old baby, and arrived to find a team of 10 with one phone, no computer and no finance person. They were spending donations they hadn't received yet. When I left three years later, it was double the size and actually had a strategy.
In 1990, I joined Amnesty International UK as director - another huge leap in responsibility. I had to learn how to relate to presidents and prime ministers, and to approach people for £1m donations.
I've been at Unicef UK 10 years, with a unique level of access and influence. At the London summit in April, we lobbied for investment by the G20 in social protection for children, and in its communique it allocated $50bn. There's nothing better than going to work knowing that you're helping to make that kind of difference.
David Bull is executive director of Unicef UK