Providing people with information is considered an important first step in encouraging them to behave sustainably as it influences their consumption beliefs, attitudes and intentions. However, too much information can also complicate these processes and negatively affect behaviour. This is exacerbated when people have accepted the need to live a more sustainable lifestyle and attempt to enact its principles. Drawing on interview data with people committed to sustainability, we identify the contentious role of knowledge in further disrupting sustainable consumption ideals. Here, knowledge is more than just information; it is familiarity and expertise (or lack of it) or how information is acted upon. We find that more knowledge represents a source of dilemma, tension and paralysis. Our data reveal a dark side to people’s knowledge, leading to a ‘self-inflicted sustainable consumption paradox’ in their attempts to lead a sustainable consumption lifestyle. Implications for policy interventions are discussed.