I know this sounds philosophic and a bit religious so far, but let me explain. Consider these examples:
1) You are presented with a documentary about starving children in a third world country. The film presents statistics, descriptions, and difficult-to-look-at imagery. I believe most of us will be moved by being exposed to such content. But, this phase will most likely pass within a week or so and there won't be a lasting impact on our behavior or passions.
Now, consider actually visiting this country personally and seeing all the suffering, pain, and death firsthand. Imagine seeing these children dying, suffering, and starving in your very presence. In contrast, this experience will be magnitudes more powerful and you are much more likely to be deeply affected by what you see and feel. A direct experience like this could move someone to act and start fighting towards decreasing such suffering.
2) You read a series of articles or a book on the most heavily polluted areas in the world. You are presented with information on Chinese and Indian cities, various third world countries, and even neighborhoods in the U.S. Let's also assume you see imagery and videos of the effects of the pollution on the environment and the people that live in these cities.
Now, let's transport you to a heavily polluted city in China where you are coughing incessantly, your eyes are burning, and you have to wear a breathing mask to be able to actually get through the day. At the end of the day, you feel nauseous, exhausted, and overall very sick. Let's assume you live through such conditions for at least a week to get a small taste of how your life would be in such a location. Compare the difference between simply reading about an issue and actually living through it. Direct experiences are much more likely to affect you at a deep level and move you to act.
3) This one is a real example. Consider the case of Roger Boisjoly. He was a NASA engineer that worked on the launch of the space shuttle Challenger. Boisjoly " found disturbing the data he reviewed about the booster rockets that would lift Challenger into space. Six months before the Challenger explosion, he predicted "a catastrophe of the highest order" involving "loss of human life" in a memo to managers at Thiokol." Boisjoly was quoted saying "I fought like Hell to stop that launch. I'm so torn up inside I can hardly talk about it, even now."
As a result of this experience, "Boisjoly traveled to engineering schools around the world, speaking about ethical decision-making and sticking with data. "This is what I was meant to do," he told Roberta, "to have impact on young people's lives." For his whole life, he fought to promote a cause he believed in. What if Boisjoly was a NASA engineer that wasn't directly involved with this launch but had read about the events that took place. What if he had read about other engineers that had tried to stop the launch but had failed, would he still have fought for the cause he did? Perhaps. But, I believe his powerful experience and direct involvement are what pushed him towards fighting for what he believed in. His experience had a life-long effect on who he was and what he wanted to do.
I know that I probably stated the obvious in this post but I believe we (people living in prosperous countries) often forget how truly disconnected and sheltered we are from a lot of terrible problems. We don't directly experience situations that have the potential to move us and awaken our passions. We generally lack experiences that make us want to truly and fully fight for something we believe in. It's fortunate that we can live in such favorable conditions and not suffer. However, it's also unfortunate because we are truly disconnected from many of the world's problems.
Quote source: http://www.npr.org/blogs/thetwo-way/2012/02/06/146490064/remembering-roger-boisjoly-he-tried-to-stop-shuttle-challenger-launch?sc=fb&cc=fp