The Seldinger technique is used in nearly every cardiovascular procedure to gain safe access to the inside of a blood vessel.

First, we puncture the vessel with a needle. Then we carefully thread a wire inside the needle, so it forms a safe channel to the inside of the vessel. From there we can pass larger catheters or devices over it.

In the beginning, I had difficulty with threading the wire, and it took me several tries before I finally realized why it was a challenge for me.

Because I was so preoccupied with aiming the needle at the artery, I would let my guard down and prematurely celebrate my success when it entered and blood came rushing out. In that moment, the needle would move before I could thread the wire. “Losing access,” as we refer to it, is generally harmless, but means starting the procedure over.

All surgical residents learn throughout their training that some of our biggest mistakes take place as soon as we let our guard down.

These moments tend to come right after successfully pulling off something challenging and anxiety-provoking. We think we are safe because the hardest part is over, but a sigh of relief can be the most dangerous moment in surgery.

When the coronavirus crisis first emerged in this country, we were alert. I tuned in to the news multiple times a day, and paid attention to every detail in my surroundings as if I were getting ready for the most difficult part of an operation.

As weeks have gone by, thanks to our vigilance, there have been many moments of progress: patient success stories, infrastructure advancements, community support, and varying degrees of promising research. Some of the models seem to suggest we have passed the peak of the pandemic and are now entering the containment phase, although this varies from region to region.

I feel this shift psychologically, too. I observe my behaviors changing. And I feel uneasy because I know I have experienced this kind of change before.

We have to be wary of developing too much of a sense of security or complacency with the virus. Many of us are collectively breathing a sigh of relief because we believe that we have weathered the initial impact of the pandemic. It feels easier to joke about it or to relax our strictness regarding social distancing. “Quarantine fatigue” has begun to undermine our resolve.

I worry that we are celebrating prematurely. The needle may be in, but the wire is not. This is our time to steady our hands and sustain our focus, instead of letting our guard down. Models are predicting a sharp rise in the expected daily death tolls with the reopening of the economy and easing of social-distancing measures.

Because if we lose our drive and attention here, we may have to start all over again.

This time, the virus will already be within our communities. Our reserves will be at an all-time low to deal with the demands of the pandemic, as we have grown impatient with limitations in resources and freedom, while becoming weary with feelings of loneliness and restlessness. As with procedural complications, the second time is always more challenging.

Jason Han is a cardiac surgery resident at the Hospital of the University of Pennsylvania. The opinions expressed in this article do not represent those of the University of Pennsylvania Health System or the Perelman School of Medicine.