Design and Communication Considered Biggest Software Challenges
I just stumbled across this great top ten software lessons learned list. I was happy to see the first one on this list: Object orientation is much harder than you think. I would probably state this as, "Software design is much harder than you think". Regardless, it's a very important point. Writing code to perform simple tasks is easy. Writing code that's well designed so that the code is changable, maintainable, and readable is very challenging.
Number two on the list is equally as important: The difficult part of software development is [human] communication. Alistair says it best, "remarkably few people in our field have devoted serious energy to understanding how these things called people affect software development... the software development community has largely ignored the characteristics of people as a topic of study. This is a significant oversight, akin to ignoring iron in walls and wondering why radio experiments are not giving the expected results." On a related note, I was very happy to recently learn that the architect on my team has a degree in cultural anthropology!