Think about somebody you love. Are you doing it?
Now think about them on fire, and you’re holding a bucket of water. Your course of action is easy and obvious.
Now think about 1,000 people on fire and 1,000 other people holding buckets of water. You use yours and yell for others to do the same, but for some bizarre collection of reasons many of them don’t. People fight over and spill some of the buckets, etc.
Now think about four billion people on fire and 4 billion other people with