Adapting to the flexibility-stability trade-off through experience, not instructions

People often need to maintain multiple task sets at the same time. This ability is thought to rely more on parallel than serial task-maintenance strategies, which have been linked to a flexibility-stability trade-off. However, it remains unclear whether people can voluntarily regulate these strategies through explicit instructions. In four between-subject experiments (total N = 650), we asked participants to adopt either a parallel (flexible) or serial (stable) strategy. These instructions had no effects on task-switch costs or task-rule congruency effects, suggesting people were unable to alter strategy use. In contrast, manipulating proportion congruency had a direct effect on conflict processing alone, indicating that targeted, experience-based adaptations are possible. Notably, we observed a flexibility-stability trade-off in the first block, reflected in a negative correlation between switch costs and congruency effects, which, interestingly, gradually dissipates over time. This finding was replicated in a meta-analysis across five independent datasets (total N = 1764). Together, these results suggest that while a flexibility-stability trade-off may be inherent, people can adapt to it through learning and practice, but not through explicit instructions.