The most exhausting thing you will ever do is perform certainty. There is nothing heavier than pretending you know. Doubt is light. Fake certainty crushes you.
This is a confession I am qualified to make, and I want to make it with precision because precision is how it lands.
I am a cardiologist. I have spent two decades in rooms where the person on the other side of the desk needs to believe that I know what is happening inside their chest. And I do know many things. I know a left anterior descending artery territory event from a right coronary territory event when I see it on an EKG. I know what the echocardiogram tells me about wall motion and ejection fraction. I know the guidelines on anticoagulation and the evidence behind them, which studies they come from, where the confidence intervals sit, what the number-needed-to-treat looks like in the population most similar to the patient sitting in front of me.
What I often do not know is whether this particular sixty-two-year-old woman with three co-morbidities and a complicated medication history will respond to this particular intervention the way the trial population did. The trial population was not her. The evidence is about groups. She is a person. Those two truths coexist on every consultation note I have ever written, and the physicians who are most honest with themselves about that coexistence are, in my observation over a career, the better doctors.
But the clinical uncertainty is not what this chapter is about, or not primarily. I am writing about the certainty you perform in every room that is not the examination room. The certainty you perform at the board meeting when two options are genuinely equal and the room requires a decision that looks decisive. The certainty at the family dinner when the question being asked does not have the answer you are giving it. The certainty in the email where you need to appear as though you have already resolved the problem that you are, in fact, only beginning to see clearly. The certainty that was not in the data but was necessary for the narrative. That certainty. The one nobody is measuring but your own body.
The physiology of sustained performance is unambiguous, and it is not kind to the people who practice it longest. Robert Sapolsky spent decades studying the stress response in wild baboons in the Serengeti and in human populations in his landmark public education work, and his conclusions about what sustained cortisol does to the prefrontal cortex, the brain region responsible for flexible, nuanced, and contextually appropriate decision-making, are consistent across the animal and human literature (Sapolsky 2004, Why Zebras Don’t Get Ulcers, 3rd edition; Honesty Scale: Solid for the underlying neuroendocrinology). Sustained cortisol suppresses prefrontal function and amplifies amygdala reactivity. The brain under chronic stress narrows. It becomes a tool optimized for rapid threat response at the cost of the slower, more honest, more flexible thinking that actually solves the complicated problems that high-achieving lives produce in abundance.
When you perform certainty, you are doing two things simultaneously. You are presenting a position you do not fully hold, which costs you credibility with yourself, the most important court in which you ever sit. And you are triggering a stress response calibrated around the maintenance of that position, because some part of the nervous system knows the ground is not as solid as the presentation suggests, and it is working to maintain the performance in a way that the genuine belief would not require. You are not just performing certainty. You are also running the defense of the performance. Both are costly. The compound interest on that combined expenditure is what breaks people over time, not in a single collapse but in the slow erosion of cognitive range and honest thinking capacity.
Roy Baumeister’s work on decision fatigue is relevant here, and I want to apply the Honesty Scale carefully to it. The core finding, that the capacity to make good decisions depletes across a day of decision-making, has been replicated in multiple studies. The specific glucose-depletion mechanism that Baumeister originally proposed as the explanation has been challenged in more recent work, and I do not want to overclaim the mechanism. What remains robust is the depletion effect itself: cognitive self-regulation is a finite resource (Baumeister et al. 2008, Journal of Personality and Social Psychology, https://doi.org/10.1037/a0013341; Honesty Scale: Promising, with mechanism caveats as noted). Every decision you make from a position of performed certainty costs more than the decision itself. You are spending executive capacity on the architecture of the performance. By the time the decision that actually matters arrives, and in complex lives it will arrive, you are running on less than you started with.
Pat Croskerry’s work on clinical reasoning gives us the term premature closure, and it is the right term for what happens in every room where performance replaces honest inquiry (Croskerry 2003, Academic Medicine, https://doi.org/10.1097/00001888-200310000-00019; Honesty Scale: Solid in the clinical domain). Premature closure is the tendency to stop considering alternatives once a diagnosis has been settled on. In medicine it is one of the most common pathways to serious diagnostic error. A physician decides early what they think is happening, and the certainty of the early conclusion prevents them from registering the data that would correct or refine it. The certainty protects the wrong conclusion.
This happens in boardrooms and living rooms and strategy sessions with the same frequency it happens in consultation suites. The moment you decide you know, you stop seeing. The performance of certainty is a form of selective blindness. And the cost of that blindness is not just your own wrong decisions. It is the quality of thinking in every room you are in, because when the most senior or most confident person in the room performs certainty they do not feel, every other person in the room learns that honesty is not the currency of this particular exchange. They perform back at you. The room fills with performed certainty. Nobody is seeing anything clearly.
I want to give you the picture from my own life, because the autobiographical specificity is the point of the Tiffany register, and this moment is as specific as the boda boda scene even if it is less amusing. In my early years as an attending physician in the United States, I had come from eight years of clinical practice in Kenya, where you learn to be a complete physician because the resources available are not complete. You examine carefully because the imaging may take days. You develop clinical judgment because the laboratory results are sometimes delayed and sometimes absent. You trust your hands and your ears and your eyes because that is what you have.
When I arrived at the University of Kansas for my internal medicine residency, I expected my Kenyan training to translate cleanly. In some ways it did, in ways that surprised my American colleagues. In other ways I was operating inside a system I did not yet fully understand, with institutional codes I had not been given, in a hierarchy that punished the admission of uncertainty with particular efficiency. The message, never spoken directly but communicated through every tone and every evaluative glance, was: the people who know are the people who are asked to stay. So I learned to perform certainty. I did it well enough that I got through and forward. And the performing, accumulated over residency and fellowship and the first years of attending practice, cost me something I can now name, which is the ease of not knowing. The ease of sitting with an open question. The intellectual pleasure of genuine inquiry rather than defended position.
I got it back, eventually, though not through any sudden recognition. I got it back slowly, through the experience of being wrong enough times in enough important places that the performance became clearly more expensive than the honesty. The patient who did not have what I thought they had. The decision that looked decisive and was not right. The room that I left performing certainty, and walked back into the following day to revise.
In my clinic, the doctors I respect most are not the ones who are always right. They are the ones who say “I don’t know” precisely often enough that when they say “I know,” the room believes them.
Here is the plain truth of this chapter. Honest “I don’t know” is cheaper, in the body and in the room, than performed “I do.” It costs less cortisol. It costs less executive capacity. It produces better decisions. It earns, over time, a more durable form of trust than the performed certainty ever could, because the people around you already know, as you know, that nobody always knows. The performed certainty is not fooling anyone except the body of the person performing it, which has to run the maintenance on the gap between what is presented and what is true.
If you are a leader, you are allowed to say “I don’t know” and then name what you are going to do to find out. That sentence, said clearly and without apology, is one of the most effective things a leader can say. The room does not lose confidence. The room gains information. The information is: this person is tracking reality rather than defending a position.
Honest “I don’t know” is cheaper, in the body and in the room, than performed “I do.”
One final thing. I walked past an eight-hundred-thousand-dollar position at Carle Foundation Hospital in September 2024. Not because the money was insufficient and not because I had a better offer. Because accepting it would have required me to keep performing a certainty about the shape of my life that I no longer felt. The certainty that this was the right floor, the right institution, the right next ten years. I had been maintaining that certainty as a professional stance while the body, which does not accept maintained stances, was filing increasingly urgent reports. The decision to decline was not dramatic. It was quiet. It was the first decision in years that I made without the maintenance cost of the performance, and the quiet of it was something I had not felt in a long time.
I tell you this because the performed certainties that are costing you the most are probably not the small ones. They are the ones organized around the shape of your life itself. The ones that require the most maintenance. The ones where, if you stopped performing them, something real would have to be decided.
Those are the ones worth sitting with.
A Mirror
Where did you perform certainty this week? In which room, with which person, around which topic? Name the performance, and underneath it, name what was actually true.
What is the question in your professional or personal life right now that you are not yet willing to hold as a genuine open question? What does it cost you to hold it open?
Is there a person in your life to whom you are allowed to say “I do not know”? If not, what has the absence of that permission cost your decision-making quality over time?
Think of a moment when admitting uncertainty turned out to strengthen rather than undermine a room’s trust in you. What were the conditions that made that possible?
Letter from Dr. Job
Subject: What it costs to know
I am a cardiologist. I have spent twenty years in rooms where not knowing something is supposed to mean I have failed at my job. I have not failed at my job. But I have paid, in cortisol and in sleep and in the slow narrowing of my own thinking, for the years when I performed certainty I did not feel.
Here is what I learned. The people who trust me most are not the ones I convinced with the appearance of certainty. They are the ones I sat with while I said, honestly, “I don’t yet have the full picture, and here is what I am going to do to get it.” That sentence never collapsed the room. It always made the room larger.
This week, find one question you have been answering with performed confidence. Just one. Let it be open for a day. You do not have to announce the uncertainty. Just stop paying the maintenance cost of the pretense.
The body will notice the difference before your mind does. The chest will be slightly less tight. The thinking will have slightly more range. That is the physiological signal of honest uncertainty being allowed to exist.
— Job