The discussion about expectation-building is based on a critical assumption. It assumes that new experiences are like old experiences (or in other words, that the expectations we build turn out to be true). But what happens when our expectations turn out to be wrong? As the saying goes, there is an exception to every rule. What happens when the type of sushi you always enjoy tastes bad to you one night?
When your expectations fail, you know that your theory-of-sushi needs to be adapted. If your theory was perfect, after all, you would never have generated an incorrect expectation. When faced with expectation failures, we, logically enough, attempt to repair the structure that generated the expectation. But this is not simple to do. Since many different memory structures provide expectations at any one time, how do you know which of those structures needs work? When your sushi tastes bad, do you fix the ordering scriptlet or the eating scriptlet? Perhaps neither of these scriptlets need to be changed. Perhaps you need to add an addendum to your restaurant MOP which tells you not to go out for food when you have a bad cold.
Explanation lies at the root of how you know which knowledge structures need to be repaired. You need to explain the failure to yourself. You might determine, for example, that the cause of the bad sushi was the fact that the fish was old. Such an explanation tells you which structures to update. Here, you might index this case under the expectation in the sushi MOP that you expect to enjoy the sushi. You might also index this case under your ordering scriptlet with the admonition to check how old the sushi is before ordering it. Whenever you reach a tentative explanation, you use the explanation to index the case under the appropriate knowledge structures.
When we experience a number of failures that have the same explanation and point to the same knowledge structure, we then refine that knowledge structure. Imagine you have bad sushi again, and again the explanation is that the fish was old. When indexing this case, you will come across (i.e., be reminded of) your previous experience. On the basis of these matching explanations, you will build a generalized knowledge structure which indicates that when sushi is old, it is bad.
Cases and the Process of Fixing a Broken Generalization
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