The Ant and the Grasshopper
The Ant knew that food would be hard to come by in the winter, so one hot summer day, as the Grasshopper frittered away the day leaping and dancing and making merry, the ant thought of nothing but gathering food for the hive. It even hoped to save enough food for the Grasshopper, who was not responsible for an upbringing and genetic makeup that gave it insufficient Conscientiousness.
The Ant focused so completely on gathering food, making its route more efficient, carrying the most efficient load possible, that it missed the shadow that fell over it mid-afternoon. The Anteater's tongue sprung out to carry the Ant to a waiting, hungry mouth. The Ant was delicious.
Meanwhile, a Black Swan ate the Grasshopper. The Grasshopper was even more delicious, having feasted on a variety of treats during its short but pleasant life.
-Not Aesop's Fables
I'm trying to figure out what the important problems are in the world so that I can figure out what I should do about it. But there are a few very different ways the world could be. Depending on which is the case, I might want to do very different things to save the world. This is an enumeration of the cases I've thought of so far.
I'll start with existential risks, because they have the potential to affect the largest number of people.