Fast fashion, with its focus on cheap clothing and everchanging trends, has an enormous negative environmental and social impact. Despite rising consumer awareness and slow fashion as an emerging trend, many consumers often still rely on fast fashion. This research aims to create insights into why customers keep returning to fast fashion and what is holding them back from buying sustainable fashion. This is done through a quantitative survey (n=521) and qualitative semi-structured interviews (n=9). Based on the findings, opportunities are defined for designers on how, where, and when to intervene, and on which target group to focus. The main obstacles that counter slow fashion are (i) a lack of understandable and clear information, (ii) the price or available budget, and (iii) the importance of social influence. Strategic design interventions should focus on educating eco-conscious and social-conscious customers based on their personal definition of sustainable fashion. By providing in-store information during time of purchase, designers can create new shopping experiences, educate customers using a positive note and build customer relations with the retailer. Further research should extend these insights with retailers' perspectives.