Ask HN: What should I learn as a product manager with tech background?

I've recently switched from being a developer to a product manager, so from the triad of tech, design & business, I have a good background in tech.

Now, I don't know what I don't know. I'm seeking resources (books/blogs/blog posts/...) about the other two domains, which allow me to be an excellent product manager.

While I have a habit of checking Hacker News nearly every day for the last 8 years, what I appreciate the most is a community like Hacker News for product managers.

Thank you very much :)