Proactive behavior, which should be anticipatory and agentic, can be defined as actions focused on certain behaviors aimed at improving job performance, career success, and employee well-being. Even if organizational citizenship behaviors have been frequently characterized as proactive behaviors, this is not true under every condition, as they may be either reactive or passive. Although proactive behavior among employees has been widely studied because of the importance that organizations place on improving performance and effectiveness, the potential and possible negative outcomes of such behavior have often been ignored. Examining and discovering the potential negative implications of proactive behaviors and formulating strategies to manage blind spots are vital for developing a general understanding of proactive behaviors for both employees and firms. The intention of this study is to conduct a literature review on proactive behaviors by focusing on the dark side and blind spots of proactive behaviors. This chapter also explains various forms of proactive behaviors and theories that can effectively describe the negative outcomes of such behaviors and discusses the detrimental effects of proactive behaviors on both employees and organizations.