Every clinician has encountered this moment. A patient leans forward and says, “But doctor, I was fine yesterday.” The statement carries confusion, frustration, and sometimes quiet alarm. It also reveals an assumption deeply embedded in both medical culture and human cognition, that stability should look like consistency.
In clinical medicine, predictability is often mistaken for stability. We feel reassured when symptoms follow familiar patterns. Patients feel encouraged when treatments produce repeatable responses. Variability, by contrast, generates unease for everyone involved. Yet predictability and stability are fundamentally different properties. Predictability concerns whether outcomes can be anticipated. Stability concerns whether a system can tolerate variation without losing coherence.
Medicine, like much of human perception, quietly equates consistency with security. When expectations are repeatedly met, we infer stability. When patterns shift, discomfort often exceeds the magnitude of the change. But this is a cognitive error. Stable biological systems fluctuate constantly. Blood pressure varies. Energy levels shift. Symptoms wax and wane. In health, variability is not abnormal. It is intrinsic.
The erosion of expectation
The difficulty arises when predictability erodes in ways that challenge previously reliable assumptions. Chronic illness makes this especially visible. A patient with multiple sclerosis describes a familiar pattern: several relatively good weeks followed by difficult days. Nothing new clinically. No relapse. No measurable disease progression. Yet the distress is real, because variability now violates expectation more than physiology.
Fatigue is no longer just fatigue. A missed activity is no longer just inconvenience. A canceled plan is no longer just scheduling noise. Variation becomes signal.
Patients search for explanations. Clinicians search for causes. Both attempt to interpret fluctuations using frameworks built around predictability. This is where the confusion becomes consequential. When stability is defined by predictability, variability feels like failure. But when stability is understood as adaptability, variability becomes expected.
The illusion of control
Human systems, including bodies, identities, and functional capacities, are inherently dynamic. They compensate, recalibrate, and reorganize. Chronic illness rarely invents instability. Biology was never stable in the mechanical sense. What chronic disease does is remove the illusion of predictability we unconsciously relied upon. Symptoms fluctuate. Capacity shifts. Responses vary. Chronic conditions do not introduce variability so much as they amplify our awareness of it.
Yet our perceptual habits remain biased toward expecting consistency from systems designed for fluctuation. This mismatch generates a subtle but persistent strain: Patients interpret variability as deterioration, while clinicians interpret it as a loss of control. Uncertainty becomes indistinguishable from instability.
But unpredictability alone does not define instability. A stable bridge sways under load. In fact, rigidity, not movement, is what leads to structural failure. Stable ecosystems oscillate within ranges. Stable physiology adapts within limits. What matters is not whether variation occurs, but whether that variation destabilizes the underlying structure.
Reframing the metric
In clinical practice, much of the distress surrounding chronic conditions arises not solely from symptoms, but from violated expectations about reliability.
- “I was fine yesterday.”
- “This used to work.”
- “I do not understand why this keeps changing.”
These are not merely emotional reactions. They are cognitive responses to disrupted predictability. When predictability fades, mental energy shifts from living to evaluating. Patients become hyper-attuned to fluctuation. Clinicians become hyper-focused on explanation. The burden is not purely physical. It is perceptual, a cognitive tax imposed by variability interpreted through the wrong lens.
Recognizing the distinction between predictability and stability offers a necessary reframing. Stability does not require the elimination of variation. It requires systems, whether clinical, psychological, or relational, capable of absorbing variability without assigning catastrophic meaning to every fluctuation.
Unpredictable symptoms do not automatically imply decline. Variable capacity does not signal failure. Fluctuation is not synonymous with collapse. Stability was never the absence of variation. It was the ability to withstand it. And variability is not the failure of the system. It is the condition of being human.
Donald Kushner is a palliative medicine physician.
