Ghost Ships

In research, we are obsessed with the idea of the counterfactual.

It’s the thing that would have happened, at the exact same moment in time, in alternative scenario. The parallel state of the world. The counterfactual helps us understand causation, because we can compare observed results to the results that we would expect if an intervention/event/treatment/program/etc had not happened. And we are obsessed with the counterfactual because nearly every empirical research question is causal. Does X cause Y? Does democracy lead to more peace? Does immigration depress local wages? Does this cause that? How do we know?

We know by creating a counterfactual world, where everything is exactly the same except X.

For example, say I am trying to understand the effect aspirin has on headaches. In order to do so, I’d want to take the difference in the severity of headaches between two states of the world: the world where a person took the pill (the real state of world), and world where the same person never took the pill (the counterfactual state of the world). The difference between those two dimensions, at the same point in time, represents the effect of the intervention itself. In this case, the aspirin. If we knew how this same person reacted in both situations, and furthermore, if there was a difference in those reactions, we would be able to reasonably infer the causal effect of aspirin. 

But of course, there is a fundamental problem. 

If the first thing you learn in statistical methodology is “correlation does not equal causation,” then the second is “the fundamental problem of causal inference.”  We only are able to  observe one version of the world. We can never actually observe the true counterfactual. It doesn’t exist. You either take the aspirin, or you don’t. The only thing we will ever observe is the action, or the non-action, but never both. Which means that we can never be certain that something has a true causal effect.

Now, throughout my master’s program I’ve learned about a plethora of fascinating statistical tools and research designs that address this very conundrum. There are lots of ways to “construct” a counterfactual in research. We can include a comparison group in a randomized control trial. We can do a comparative case study. We can control for different confounding factors, or assume parallel trends, or exploit a natural phenomenon that creates a quasi-experiment. The better our counterfactual, the more valid our estimate of causal impact will be. So, it makes sense, really, this counterfactual obsession. 

And frankly, it’s been satisfying. To discover this way to create the alternate reality. 

Because this fundamental problem isn’t just relegated to researchers. We all obsess over these questions. 

What if that bartender had won the lottery? What if your friend from high school had never moved away? What if Neo had taken the blue pill? What if we chose Door A instead of Door B? It’s a hallmark of the human mind. “What if…?” Haven’t we all thought about how life would be different had one single event been changed?

When we do this, we are indulging in counterfactual reasoning.

But unlike in research, there’s no statistical method that can create the “Sliding Doors” version of our own lives. No randomized control trial for a major decision. No control group to observe the other outcome. The only path we can know is the path we decide to take.

I’ve been thinking about the counterfactual a lot. It’s hard not to in a year like this year. And I was up late, finishing up a term paper, when I remembered something I had read last year.

It was from Cheryl Strayed’s book, “Tiny Beautiful Things.” It’s a collection of letters and responses from her “Dear Sugar” advice column. 

In the column, Cheryl Strayed writes anonymously as Sugar. Over the years, she responded to an array of questions from readers all over, who were seeking advice about anything and everything. People who couldn’t pay their bills, people who lost parents, a woman who couldn’t muster the courage to finish her novel, a man who couldn’t decide if he wanted children. Sugar answered questions on sex, love, drugs, agony, ecstasy, trauma, joy, poverty, addiction, petty fights and 30-year grudges, fears, friends, family and all the tiny beautiful things in between. 

But there was one line, from one particular letter, that was left wedged in my brain.  

“I’ll never know and neither will you of the life you don’t choose. We’ll only know that whatever that sister life was, it was important and beautiful and not ours. It was the ghost ship that didn’t carry us. There’s nothing to do but salute it from the shore.”

Sugar is writing in response to a man who had a big decision to make - a choice. Either choice is equally admirable, so there is no right or wrong answer. But the decision is big, and emotional, and life-changing. So Sugar asks him to imagine the parallel lives. And she names that alternative life the “ghost ship.” The life we could have had, but didn’t. 

It’s the counterfactual. 

But a less sterilized, more poetic, version of it. 

And I’d been thinking about this idea a lot lately - what if we had stayed in San Francisco, what if I didn’t go to back to school, what if we had decided to have kids, what if we made the *other* big life-changing decision instead.

We all have that parallel life, the path not taken, the road not traveled. We can all imagine the sister life. The ghost ship.

I think some people might find this quote sad. When the loss of would-have-beens hangs thick in the air. And it’s hard to salute that life from the shore, when you aren’t yet entirely sure how to fully unmoor the ship that never carried you. 

For me, though, I find this idea of a ghost ship reassuring and reaffirming. Because the way I read it, it is a nod to regret. Acknowledging you’ll likely have it. Acknowledging there will always be unanswered questions, and that you’ll never know what you don’t know. 

But it’s also about trusting your gut. And about leaving guilt at the juncture where you made your choice, where you boarded one ship instead of the other. It’s about throwing that guilt out to sea. Those big decisions, they do define the paths that we take, but that doesn’t mean that the life we would’ve had if we’d made that other choice doesn’t have meaning and value. 

Maybe the counterfactual doesn’t exist, but the ghost ship does. I can still ask the what if’s of the other “life.” But then, I can wave at it as it sails by, and choose to fully embrace the life I have, and the life I have chosen.

Because this ship is where I am supposed to be.