It says when trying to figure out what to study, think about what might give you most options for the future, a future that you might have almost NO way of predicting now. He calls this "staying upwind." He gives an example:
Suppose you're a college freshman deciding whether to major in math or economics. Well, math will give you more options: you can go into almost any field from math. If you major in math it will be easy to get into grad school in economics, but if you major in economics it will be hard to get into grad school in math.
And given a choice between studying two subjects that interest you, but one is easier for you and one is a bit harder (but still within your abilities), opt for the harder one:
The best protection is always to be working on hard problems. Writing novels is hard. Reading novels isn't. Hard means worry: if you're not worrying that something you're making will come out badly, or that you won't be able to understand something you're studying, then it isn't hard enough. There has to be suspense.
You don't have to automatically agree with everything in his essays as Great Truths, but it's worth considering his ideas.