"How do you prove to others?" The point of writing is to express an idea. You prove this to others by providing relevant metaphors (with respect to the subjec

"How do you prove to others?" The point of writing is to express an idea. You prove this to others by providing relevant metaphors (with respect to the subject, and to the intended audience), supporting ideas or evidence, and tie everything together into a concise, organized format. "How do you tell if your writing is good quality?" People listen. People take your opinion seriously. People respect you, and mimic your ideas or style of writing. The evaluation of writing quality is almost always a subconscious process, since analyzing communication itself is somewhat meta. "it's really easy to evaluate technical skills like coding" It's easy to evaluate coding, in some sense, because it's easy to communicate to a computer. Humans are much better than computers at thinking, communicating, evaluating, and responding to their input. So no, evaluating writing is more difficult and more subjective than evaluating coding ability.