EA Global was dominated by talk of existential risks, or X-risks. The idea is that human extinction is far, far worse than anything that could happen to real, living humans today.

"Once I identified that this is the most important thing I could do with my life, I started consciously looking for opportunities to push this X-risk ecosystem forward," says Tallinn. He has helped start the Centre for the Study of Existential Risk and the Future of Life Institute, and contributes about $500,000 each year to research.

Suppose you think that reducing the risk of human extinction is the highest-value thing you can do. Or maybe you want to reduce "x-risk" because you're already a comfortable First-Worlder like me and so you might as well do something epic and cool, or because you like the community of people who are doing it already, or whatever.