The connection between attitudes and sustainable behavior is important and has been researched from several perspectives. However, we still lack comprehensive knowledge of the factors influencing their relationship. We address that gap by examining the impact of perceived impact and prior knowledge on the connection between attitudes, intentions, and behavior. We sampled 464 participants from Finland and Sweden and demonstrated that positive attitudes significantly predict behavioral intentions, with prior knowledge and personal impact moderating that relationship. Prior knowledge also moderates the relationship between attitudes and actual behavior, but personal impact does not. Additionally, while attitudes do not directly predict behavior, behavioral intentions reliably forecast actual behavior, underscoring the importance of fostering positive intentions for promoting sustainable practices.