We’ve studiously avoided talking about requirements for expert systems because it is such a small niche of software development. Please let us know in the comments on this post if this is an area you would like to read more about. This post is both a discussion of the main barrier to success for these systems and an introduction to future posts if you ask for them in the comments on this post. Expert systems, or AI programs can solve some of the hardest problems. Yet AI software has not dominated the software landscape, neither Heinlein’s nor Vinge’s fictions have become real. Why has AI software failed? It isn’t that the hardest problems are too hard to solve, it’s that they often don’t need to be solved at all.