I'm really good at learning new things from scratch but I'm not sure what would be the best use of my time. I've started learning machining and web design but I can't help but feel like there's something more valuable that I could be learning instead. What's something that's so hard to learn that learning it will instantly provide me with a high-level marketable skill without having to go to college? I can probably learn it in half the time most people who already have learned it did. Linear algebra?

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