My undergraduate degree was math. Looking back, I find it really hard to imagine how I could have learnt all that without going to college. I just don't think it's possible to recreate that combination of extrinsic motivation and interactive learning. maybe moocs can do this but I suspect they fall short on both accounts.

Now I'm able to learn more independently (e.g. type theory and HoTT) but it's still very difficult and I don't think I could do it without my undergraduate and higher degrees.

I see a lot of posts on hn asking the lines of "how can I learn X on my own". Without at least some formal education in college math or cs, I suspect the answer may be "it's not possible "