Ask HN: What do you wish you knew about UI/UX design?

I'm a UI/UX designer interested in writing about design. I've written about the principles of iOS design, a case study on how I designed an iPhone app, etc., in my blog (http://radesign.in/blog/).

Instead of writing what I think is useful I want to write what the audience finds useful. So, what about UI/UX design you wish you knew? What would help you? What do you find interesting? What would you like to know?