Response time is also a sensitive issue with respect to user-acceptance of an application, and certainly response time is an issue that greatly complicates implementation. In a black-box application, response time is a conspicuous issue because the end-user simply waits for the solution (or non-solution) of the problem.

One way of addressing this difficulty is to limit the amount of time spent searching for a solution, and in the case of failure, to provide an explanation for the failure. While it may be more or less easy to implement an application that satisfies limits on the amount of time needed to find a solution, it is seldom easy to implement a module that explains why the application failed to find a solution.