Writing
The act of writing demands some skills from the writer, skills of the intellectual kind. Of course, the demand varies accordingly to the type of writing among many other factors.
Writing texts for humans, from blog posts to literature, is challenging if the purpose is to convey a message in a clear and concise way, as possible.
Writing technical texts for humans and computers, also known as the act of artistic programming of digital computers, is also very challenging.
Based on typical conversations between IT professionals nowadays, I guess that only very few people alive today actually know what really entails a common communication between humans and computers through technical texts (also known as source code).