At a railway station in Washington, DC, last month, a fight broke out between a man and a woman a short distance from where I was waiting to board my train. As their voices escalated to screaming, I had a strange thought: What if one of them takes out a gun?

Last week, my mind wandered to guns again. I stumbled into a police blockade near the White House. Security forces had shut down the streets because of the annual national Christmas tree lighting. In the distance, someone started to fight with a cop. I thought about a shootout. My boyfriend asked me whether I wanted to take a short detour to see the tree. I asked if we could just leave.

I know this response isn’t rational. I write about medical statistics nearly every day, and I understand very well the concept of relative and absolute risk. I know the chances of any of us being killed in gun violence are remote, and that there’s a much greater risk of dying in a car accident or by heart disease.

Still, I didn't think about guns in Canada, my home country. I didn't think about them in other places I've lived, in Italy or the UK. I don't like that guns wander into my imagination now. It's not as much a fear of being shot that weighs on me as it is a discomfort with my newfound proximity to so many weapons. A needless threat. In the developed world, this gun problem is unique to the US — and it may eventually force me to leave. I like many things about America. I can't accept gun violence.