Premarital cohabitation has consistently been found to be associated with increased risk for divorce and marital distress in the United States. Two explanations for this "cohabitation effect" are discussed: selection and experience. We present an empirically based view of how the experience of cohabitation may increase risk for relationship distress or divorce for some people beyond what is accounted for by selection. Specifically, using a commitment framework, we suggest that some couples who otherwise would not have married end up married because of the inertia of cohabitation. We discuss practice implications for relationship transitions that are characterized more by sliding than deciding, especially where a transition such as cohabitation increases inertia to remain in a relationship regardless of quality or fit.