Effectance motivation -- a will for certainty and a feeling of being able to know and predict -- was proposed in the 1960s as the mechanism underlying the well-known attitude similarity effects on attraction (Byrne, Nelson, & Reeves, 1966). However, this motivation was largely discarded as an explanation when alternative mechanisms, such as positive affect, were identified (e.g., Byrne & Clore, 1970). The presence of alternative mechanisms need not preclude the role for effectance motivation. Therefore, the present authors investigated a sense of self-validation by the others' views as an additional mediator of attitude similarity effects on attraction. Across four experiments, self-validation mediated attitude similarity effects when measured alone (Experiment 1) and within sequential mediation patterns involving positive affect (Experiment 2A), trust (Experiment 2B), and respect and trust (Experiment 2C). Implications for multi-process explanations of attitude similarity effects on attraction are discussed.