The Most Important Words a Doctor Can Say: "I Don't Know."

The Importance of Saying “I Don’t Know”

A Fractured Tooth Far From Home

I recently spoke with a friend who was unsure what to do after breaking a tooth. Well into his eighth decade of life, he bit into a protein bar and cracked a molar below the gum line.

A fractured tooth is always a problem, but his situation was particularly inconvenient. He was away from home for a month and had to see a dentist he did not know.

The dentist explained his options. The remaining tooth could be removed, with a bridge or implant considered later. But another question soon complicated what otherwise seemed like a fairly straightforward dental problem.

My friend had undergone bilateral knee replacements.

Conflicting Advice About Antibiotics

His orthopedic surgeon had told him to take prophylactic antibiotics before any dental procedure. The reasoning was familiar: bacteria released into the bloodstream during dental work might travel to a prosthetic joint and cause an infection.

The dentist disagreed. In his view, prophylactic antibiotics were not indicated simply because my friend had artificial knees. He also preferred not to prescribe antibiotics unnecessarily.

Two doctors. Two different recommendations.

My friend called and asked what I thought.

“I don’t know,” I told him.

That may sound like an unsatisfying answer from a physician. In fact, I think it was the most responsible answer I could give him.

Why Uncertainty Matters

I had an opinion. I even thought I knew the answer. But I was a lung doctor, not an infectious disease specialist or orthopedic surgeon, and I had been retired from clinical medicine for several years. Guidelines change. Evidence evolves. What I remembered from years earlier might no longer represent current medical practice.

So I followed my “I don’t know” with something equally important:

“Let me look at the recommendations and get back to you.”

My job at that moment was not to become an instant “Answer Man,” casting a tie-breaking vote from whatever happened to reside at the top of my head. My job was to serve as a navigator through a maze of medical information and find the best evidence available.

It took only a few minutes.

Current professional guidelines do not recommend routine antibiotic prophylaxis before dental procedures simply because a patient has a well-functioning knee or hip prosthesis. I reviewed the recommendations from the American Dental Association and then looked specifically at the 2024 clinical practice guideline from the American Academy of Orthopaedic Surgeons. The message was consistent: available evidence does not support routine prophylactic antibiotics to prevent prosthetic joint infections in patients undergoing dental procedures.

I then did a quick Medline search to see whether newer evidence gave me reason to think otherwise.

It did not.

My friend now had an answer grounded not in my recollection or opinion, but in current evidence.

And it all started with three words:

“I don’t know.”

The Physician as Truth Teller

Why is saying “I don’t know” so important?

First, because it is honest. If physicians do not have reliable information at hand, patients deserve to know that. Medical knowledge is far too vast—and changes far too quickly—for any physician to have every answer immediately available.

But “I don’t know” should rarely be the end of the conversation.

There is an implicit compact between physician and patient. When the answer can be found, the physician has an obligation to look for it and return with the best information available. The patient then receives not only better medical advice but something equally valuable: confidence that the physician is a truth teller.

Over decades of caring for patients, I learned that acknowledging uncertainty did not diminish their trust. More often, it strengthened it.

“Will He Survive?”

The importance of those words became especially apparent in intensive care units.

Families sitting in ICU waiting rooms asked questions far more consequential than whether someone should take an antibiotic before a dental procedure.

“What does my husband have?”

“Will he get better?”

“Will he survive?”

Sometimes we knew.

Sometimes we didn’t.

A blunt “I don’t know” was rarely helpful to a frightened family, but disguising uncertainty as certainty was worse. The challenge was to express honestly what we knew, what we did not know, and what we were doing to find out.

“I am not certain right now, but we are doing additional testing that may provide some answers soon.”

Or:

“He is gravely ill. I can’t tell you yet how this will turn out, but we are doing everything we can, and I will tell you what we learn as we learn it.”

Those conversations establish the boundaries between what is known and the still-uncharted territory beyond it. They also change the relationship between physician and family. Instead of the old paternalistic model—the doctor possessing the answers and dispensing them to everyone else—we become partners navigating uncertainty together.

Teaching Doctors to Say “I Don’t Know”

The same principle applies to medical education.

Teaching students, residents, and fellows in the ICU repeatedly reminded me how important it was for attending physicians to distinguish what they knew from what they merely suspected.

When an attending physician confidently overstates an interpretation of a patient’s condition, junior members of the team naturally defer to that expertise. They may stop questioning. They may stop searching for alternatives. In effect, excessive certainty can dial down the collective thinking of the entire team.

But something different happens when the attending says:

“I don’t know, but I have some ideas about how we can find out.”

Now everyone starts thinking.

The resident reexamines the laboratory results. The fellow looks again at the imaging. Someone questions an assumption made the day before. Another person remembers an unusual diagnosis that might fit. Each member of the team becomes a sleuth, looking for clues that might lead to a diagnosis or a better treatment.

The attending physician has not surrendered leadership by admitting uncertainty.

Quite the opposite.

The attending has created a team.

Three Powerful Words

Medicine has changed enormously during my lifetime. We have better imaging, better laboratory tests, better treatments, and almost instantaneous access to a medical literature that once required hours in a library.

But no technology eliminates uncertainty.

Perhaps one of the most important skills a physician can develop is knowing where knowledge ends—and being willing to say so.

“I don’t know” should not mean, “I have nothing to offer.”

It should mean:

“I don’t know yet. Let’s find out.”

That is where good medicine often begins.