Between Commitment and Practice—Sustainability Attitudes and Behaviors in Spain—A Mixed-Methods Study

This sequential mixed-methods study examines when sustainability becomes a meaningful criterion in everyday consumption versus a widely endorsed discourse enacted selectively in Spain. Informed by research on the attitude–behavior gap in sustainable consumption, including work using TPB- and norm-based perspectives, the study explores how feasibility constraints and credibility concerns shape the translation of sustainability commitment into practice in a non-student adult sample. It addresses a recurring pattern in sustainable consumption research: strong normative endorsement often coexists with partial behavioral uptake, particularly when feasibility constraints (cost, convenience, perceived impact) and credibility concerns (skepticism/greenwashing perceptions) intervene. A focus group (n = 9) explored how participants define sustainability, justify conditional enactment, and interpret sustainability communication; these insights informed and refined an online survey (N = 317) capturing awareness, conceptual knowledge, concern, self-perceived behavior, practice adoption, willingness to change, and perceptions of sustainability as marketing/politics. Self-reported awareness was high (83.91%) and mean concern was 7.40/10, whereas mean self-assessed sustainable behavior was lower (6.20/10), indicating a commitment–practice gap. Most respondents reported at least one sustainable practice (98.42%) and expressed willingness to change habits (96.21%), yet intentions appeared stronger than current uptake for higher-effort changes. Associations between attitudinal endorsement and enactment were modest to moderate: concern was positively related to self-assessed sustainable behavior (Spearman’s ρ = 0.445) and to reported practice adoption (practice count; ρ ≈ 0.34), while self-assessed behavior was moderately related to practice adoption (ρ ≈ 0.48). Qualitative findings emphasized feasibility trade-offs and credibility discounting of sustainability claims. By combining interpretive evidence with survey patterns, the study shows that sustainability is widely endorsed in this sample but enacted unevenly, with feasibility and credibility helping to explain why commitment does not consistently translate into practice in the Spanish context.