Employee knowledge sharing is crucial for maintaining organizational competitiveness, and understanding its antecedents can help foster this behavior. Leaders, as key role models, play a pivotal role in shaping employee conduct within organizations. While the bottom-line mentality of leaders has received considerable focus, its impact on employee knowledge sharing remains underexplored. Grounded in the conservation of resources theory, we developed a conceptual model positioning leader bottom-line mentality as the independent variable, perceived high-performance expectations as the mediator, cognitive flexibility as the moderator, and knowledge sharing as the dependent variable. Using a two-phase survey conducted with 134 full-time employees in China and analyzing data with AMOS and SPSS, our findings reveal that leader bottom-line mentality indirectly enhances employee knowledge sharing through perceived high-performance expectations. This indirect effect is moderated by individual differences, as employees with lower cognitive flexibility show a stronger link between leader bottom-line mentality and knowledge sharing through perceived high-performance expectations. Finally, we discuss the broader theoretical and practical impacts of these findings and outline possible directions for future studies.