The approach was fine in theory, but hard-and-fast rules can rarely capture real-life knowledge. Perhaps without realizing it, we deal with exceptions to rules and uncertainties in evidence all the time. By 1980, it was clear that expert systems struggled with making correct inferences from uncertain knowledge. The computer could not replicate the inferential process of a human expert because the experts themselves were not able to articulate their thinking process within the language provided by the system.
