Why are Human-Computer Interfaces Difficult to Design and Implement? Brad A. Myers Carnegie Mellon University School of Computer Science Technical Report, no. CMU-CS-93-183. July 1993. A revised version appears as: "Challenges of HCI Design and Implementation," ACM Interactions. Vol. 1, no. 1. January, 1994. pp. 73-83. Everyone knows that designing and implementing human-computer interfaces is difficult and time-consuming. However, there is little discussion of why this is true. Should we expect that a new method is around the corner that will make the design easier? Will the next generation of user interface toolkits make the implementation trivial? No. This article discusses reasons why user interface design and implementation are inherently difficult tasks and will remain so for the foreseeable future.