Analysis of 1,252 clinic visits from 430 Parkinson's patients found that the predictability of OFF episodes—when medication effectiveness wanes—explained more variance in functional impact than traditional motor symptoms. While OFF-state motor severity and freezing primarily determined total OFF time, the unpredictability of these episodes emerged as the strongest predictor of how much they interfered with daily life, surpassing even tremor severity in the impact model. This finding challenges the conventional focus on motor fluctuation duration in clinical practice. The research suggests a paradigm shift toward assessing episode predictability alongside traditional measures. Unpredictable OFF periods may require different therapeutic approaches—such as on-demand rescue medications rather than timing optimization strategies used for predictable episodes. However, clinical features explained only 25.9% of OFF impact variance, indicating substantial individual variation that current assessments miss. As a preprint awaiting peer review, these findings require validation before changing clinical practice. The study's observational design from the PPMI database provides robust real-world evidence, though causality remains unclear. This represents an important step toward more patient-centered Parkinson's care that addresses the psychological burden of uncertainty alongside motor symptoms.