With the pace of change in the world, I think the most demanding aspect of most jobs would be dealing with change. There have been lots of instances in my current and past jobs where things had been done one way for a long time and now organizations are undergoing change, digitization and automation in increasingly significant ways. Recognizing and accepting that your work and your role will not be stagnant, and then embracing the change is always the most demanding. It takes time to learn and figure out new processes, and before you know it there will be yet other changes. Adaptability and agility will be key skill sets for the future.