I have to +1 'Writing essays'.
Too easily overlooked in a technical environment, but it really pays off. Both to assist in consolidating your own ideas, and also in communicating them to others.
Agreed. Also: request for canonical sources on the art of essay-writing. It's something I could use improvement on, and I don't see anything related in the best-textbooks thread.
This is the question asked by John Cook on Twitter. He lists responses from different people:
Mine are: quantum mechanics, Python, cooking, the language of philosophy.
What learning curve do you wish you'd climbed sooner? Give reasons and stories if you feel like it. Do you think other people should climb the same curves?