Despite the prevalence of career insecurity, the research about it is only at the beginning stage. Existing studies mainly portrayed it as a “toxic” phenomenon, focusing on its negative influence on work and career outcomes. Based on the control model of self-regulation, the current study aims to challenge this view by revealing its opposing effects on proactive career behavior, which is critical for long-term and sustainable career success. We argue that career insecurity reflects a perceived discrepancy that one’s current career path deviates from the desired one, which triggers a “discrepancy-reduction” process in which people more reflect on past experiences and then engage more in proactive career behavior and an “expectancy-assessment” process in which people downward regulate their career confidence and then engage less in proactive career behavior. Furthermore, adopting a goal hierarchy perspective, the model argues that self-relevant goals influence specific regulation strategies. We thus propose that self-esteem, which describes to what extent people desire to build a positive self-perception, would enhance the positive indirect effect and buffer the negative indirect effect. Through an online recall experiment and a three-wave time-lag study, we found support for the above arguments. The findings could encourage scholars to adopt a more balanced view of career insecurity and enrich the understanding of why and when it matters.