LAUSR

BACKGROUND Epistemic uncertainty refers to situations in which available evidence is insufficient or unreliable, often accompanied by complexity due to novel contexts, multifactorial causation, and emerging options (the "unknowable unknown"). It stands in contrast to aleatory uncertainty where probabilities are known, and potential benefits and harms can be calculated and presented graphically (the "knowable unknown"). DISCUSSION Epistemic uncertainty is common, and encompasses uncertainty about the nature of the illness, whom to entrust with one's care, and one's ability to adapt and cope. Communication about the "unknowable unknown" occurs infrequently and ineffectively, and there is little research on improving communication in the face of epistemic and complex uncertainty. Terror Management Theory (TMT) predicts that in encountering serious illness, people engage in "worldview defense" - suppressing death-related thoughts, affiliating with like-minded others, and developing cognitive rigidity and intolerance of information that challenges their worldview. Mindfulness is associated with diminished defensive worldview reactions and cognitive rigidity, and greater tolerance of ambiguity. Shared mind encompasses shared understanding and affective attunement. CONCLUSION For clinicians and seriously ill patients facing epistemic uncertainty, psychologically-informed interventions that promote mindfulness and shared mind offer promise in promoting open discussions regarding prognostic uncertainty, advance care planning, and treatment decision-making.