Background To understand whether patient‐reported experiences with lung cancer may create teachable moments (TM) for their relatives as evidenced by shifts in their risk perceptions, affective response, and self‐image and in turn, motivation to quit smoking. Methods Patients at a comprehensive cancer center (n = 152) completed a survey within 6 months of lung cancer diagnosis to assess their cancer‐related symptoms and openness and enumerated relatives who were smokers. Relative smokers (n = 218) then completed a survey assessing their risk perceptions, affective response, and self‐image as a smoker related to the patient's diagnosis (TM mechanisms), and their motivation to quit smoking. Cross‐sectional mediation and moderation analyses were conducted to explore the links between patient‐reported experiences, and relatives' TM mechanisms, and motivation to quit smoking. Results Relative‐reported affect was a significant mediator of the association between patient‐reported symptoms and relative smoker's desire to quit. Relatives' self‐image was a significant moderator of the association between patient‐reported symptoms and relative smoker's desire to quit, such that patients' reported symptoms were associated with relatives' desire to quit only when the relative smoker reported a generally positive self‐image as a smoker. No evidence was found for moderated mediation. However, the link between symptoms and negative affect was moderated by perceptions of risk. Conclusion Whether smokers experience a family member's lung cancer as a TM is influenced by multiple interrelated cognitive and affective factors that warrant further exploration. Clearer understanding of these factors could inform how to re‐invigorate and sustain this motivation to promote concrete actions toward smoking cessation. Copyright © 2015 John Wiley & Sons, Ltd.