Trainable skills were once a safe haven.
Before a repetitive task is automated, people can solve the same problem over and over, and get paid in proportion to how hard they are to replace.
Technology threatens to erode these positions, but despite this, some skills remain fundamental to all others.
Namely: communication and first-principles decision making.
The better you know these, the faster you can learn anything else.
Unfortunately, they're very difficult to study in isolation (without getting bogged down in a bunch of pseudo-work).
But with the right heuristics, we can get to the heart of the issue.