Rule finding is an important aspect of human reasoning and flexibility. Previous studies associated rule finding "failure" with past experience with the test stimuli and stable personality traits. We additionally show that rule finding performance is severely impaired by a mindset associated with applying an instructed rule. The mindset was established in Phase 1 (manipulation) of the experiment, before rule finding ability was assessed in Phase 2 (testing). The impairment in rule finding was observed even when Phase 1 involved executing a single trial (Experiment 2), and when entirely different stimuli and rules were used in the two phases of the experiment (Experiments 3-6). Experiments 4-6 show that applying an instructed rule in Phase 1 impaired subsequent (Phase 2) feedback evaluation, rule generation, and attention switching between rules, which are the three component processes involved in rule finding according to COVIS (Ashby, Alfonso-Reese, Turken, & Waldron, 1998).