This took me 10 years to figure out, so it's a fitting Lesson #10: What we do is not rational. Experts will come in and try to get you to develop an argument that explains why your work is important, what the need is for the work that you do, why donating to your cause is a good idea - those are important. BUT you first need to accept that what you do isn't rational. That's the only starting point that makes sense.
There is no rational explanation for dedicating your life to saving a lake. For feeding the hungry. For teaching arts to communities in need. There are rational justifications, but they don't get to the heart of it. The heart of it is .... in your heart.
Advertisers get it. They know that people make important decisions because of how they feel not because of what they know. Take a lesson from them.
The people who support your cause do it because of how they feel - about you, about the issue, about the projects.
Rationality is important to how you do your work. It should dictate your strategy, your program design, your budgeting, and your management. But every day you wake up and go to work for the crazy, wacky reasons that make sense deep inside your soul. And that's all.