The window of tolerance is one of the most practically useful concepts in the nervous system literature, and one of the least known outside clinical contexts. Developed by Dan Siegel and built upon in somatic therapy work, it describes the zone of physiological arousal in which a person can function effectively, the range within which the nervous system is activated enough for engagement but not so activated that it begins to dysregulate. Inside the window, you can think clearly, process emotions, respond proportionately, and access the full range of cognitive and relational capacities that effective functioning requires. Outside the window, in either direction, you cannot. Not fully. Not reliably.
Above and Below the Window
The window has two edges. Above it is hyperarousal, the sympathetically activated state of anxiety, panic, agitation, reactivity, and scattered attention. This is the state of too much: too much activation, too much threat-detection, too much noise in the system for sustained focus or proportionate response. Below it is hypoarousal, the dorsal vagal shutdown state of numbness, dissociation, exhaustion, and collapse. This is the state of too little: too little activation, too little engagement, the system having withdrawn from the demands of the environment because those demands have exceeded its regulatory capacity.
Both states are outside the window. Both impair function. Both are common, more common than most functioning adults recognise, because performance culture has taught people to interpret hyperarousal as productivity and hypoarousal as laziness, rather than reading both as signals about the state of the nervous system. In High-Functioning Burnout, I describe the progression from chronic hyperarousal, the wired, driven state of the high performer at full extension, to the hypoarousal collapse that is the final expression of a depleted system. The direction of travel is consistent. The endpoint is always below the window.
“The window of tolerance is not fixed. It is trainable. And the goal is not just to stay inside it, it is to expand it.”
What Determines the Window's Width
The width of the window varies between individuals and across the lifespan. It is influenced by early attachment experiences, trauma history, current allostatic load, sleep quality, nutritional status, social connection, and the cumulative effect of nervous system regulation practices. This matters because it explains why the same situation produces different responses in different people, the person with a wider window can tolerate more activation before dysregulating, and this is not a character difference but a physiological one.
The practices I describe in Somatic Productivity, breath work, movement, grounding, somatic tracking, are not primarily stress-management tools in the conventional sense. They are window-widening practices. Used consistently, they build the nervous system's capacity to stay regulated under increasing demands. The window expands, measurably, in ways that compound over time.
Applying This at Work and at Home
In a school context: a student with a narrow window, produced by trauma history, attachment disruption, or chronic environmental dysregulation, will reach the edges of their window much faster than a peer with a wider window, under the same objective conditions. The behaviour that follows is not a choice. It is the output of a system that has gone outside its functioning range.
In a workplace context: the high performer who appears to handle everything has, in many cases, built significant window width through years of regulated experience. The person who struggles under the same demands may have a narrower window, not less capacity, but a different physiological starting point that requires different conditions to be sustainable. Designing for the window means designing for the actual person rather than the idealised one. It means asking what conditions allow the people in this system to stay within their functioning range, and taking the answer seriously as a design requirement rather than a nice-to-have.
Bart Reevers