One of the most important methods that psychological scientists use to understand behavior and cognition is theorizing. Increasingly, theorizing is used to support not only additive hypotheses, but also multiplicative ones. And yet, authors often struggle to provide adequate theoretical justifications for multiplicative hypotheses. In the late 1960s and early 1970s, W. Mischel averred that, in "strong" situations, behavior is relatively uniform regardless of one's personality characteristics. In "weak" situations, that is, those that lack clear behavioral expectations, behavior is not constrained by the situation and is free to covary with personality. This is the situational strength interaction, and although this reasoning has been applied to personality-behavior models, we show that it can be used to justify many interaction models in psychology more generally. In some cases, such reasoning may serve to bolster the more traditional interaction arguments. In other cases, it shows that the traditional interaction arguments must be incorrect. In this tutorial, we describe a generalized situation strength phenomenon, called the restricted variance interaction, that can be used to pinpoint the nature, direction, and even the magnitude of many interaction hypotheses in the psychological sciences. We illustrate the value and application of restricted variance reasoning using examples from the workplace mistreatment literature and then extrapolate to several other areas of psychology. (PsycInfo Database Record (c) 2022 APA, all rights reserved).