It was the beginning of my third year of medical school. I had just started my first clinical rotation. My very first patient was Ray, a middle-aged man with pancreatitis.

I presented his case to the team. “What are Ranson’s criteria?” the attending physician asked.

My mind went blank. “Uh, I’m not sure,” I said.

“Next time, you’d better be sure,” the attending said. He turned to my colleague, who promptly gave the correct answer.

On that first day of medical training, I learned that “I don’t know” is not an acceptable answer. If you don’t know, look it up. Make it up you have to. Whatever you do, never admit that you don’t know.

Not surprisingly, doctors end up not tolerating uncertainty. In our high-tech era, this means more is done. A patient has seemingly vague symptoms, so the doctor orders some laboratory tests “just to get a baseline.” A doctor doesn’t know what’s causing the headache, so she orders a CT or MRI “just to see.” Medical students are rewarded for pursuing obscure diagnoses, so they order increasingly esoteric tests “just in case.”

This insidious practice has resulted in a culture of overtesting and overtreatment. Studies show that 30% of all medical care—at the tune of $700 million per year—is waste. Not only does this impose a heavy financial burden on society and on patients, it also results in avoidable harm. Every test has risks and potential side effects. A CT scan has a risk of radiation, for example, that may lead to cancer later in life. And one test often leads to another, even riskier, test.

Recently, my husband had an itchy rash on his arms. He mentioned this to a dermatologist friend, who recommended that he come into the office for a skin biopsy. I asked how the biopsy would change my husband’s management: regardless of what it showed, wouldn’t he still use a steroid cream? Sure, the dermatologist said, but at least we’d have more information.

Nothing against our well-intentioned friend, but this is a case where more information isn’t better. Why get a biopsy — an invasive procedure with risks including bleeding and infection — when it wouldn’t change the management or the outcome? Yet, tests are done all the time to quench the insatiable curiosity inherent in medicine: we just have to know.

Here’s another common scenario. A young woman comes in with abdominal pain. She’s able to eat and drink and looks well, but has a pain in her belly that’s bothering her. Many doctors would order a CT scan of her abdomen to make sure there’s not something bad going on. But what is this bad thing — how likely is it? How does the patient feel about the risks of the test, versus the risks of watchful waiting? If she’s fine waiting, then why expose this young person to unnecessary radiation, when it would be just as reasonable to wait to see if she gets better the next day?

More tests and better technologies are not the solution to improving clinical care. In fact, we know that 80% of diagnoses can be made without any tests at all, but by carefully listening to the patient’s story. I’m an emergency physician, yet even in the emergency setting, it is rare that a patient requires one particular test, and that test must be done right now.

Here’s what to do instead. Doctors: talk to your patients. If you’re not sure, tell them. Patients prefer honesty to false reassurance. Instead of reflexively ordering a test, discuss the benefit of the tincture of time. Remember that our first principle is to “Do no harm.” I just met two doctors, Tanner Caverly and Brandon Combs, who started an educational initiative to encourage doctors-in-training to write vignettes of medical overuse. To them, and to a growing number of physicians including the Lown Institute’s Right Care Alliance (of which I’m a proud member), preventing overuse is an ethical imperative.

Patients: insist on being an equal and active partner in your care. Ask why and how. Why is this test ordered? How will this test change my management? Make sure you know your diagnosis. Assure your doctor that it’s okay if she is not 100% sure; you don’t demand certainty, but you do expect transparency.

It’s taken me nearly ten years to unlearn the bravado I acquired in medical training and to learn that uncertainty isn’t bad; more isn’t always better; and less can be more. As the great cardiologist and humanist Dr. Bernard Lown says, you should always feel better after having gone to your doctor. We need to focus on healing by teaching and practicing the art of listening, compassion, and kindness.

Leana Wen is an emergency physician who blogs at The Doctor is Listening. She is the co-author of When Doctors Don’t Listen: How to Prevent Misdiagnosis and Unnecessary Tests.  She can also be reached on Twitter @drleanawen.