I’m terrified of losing my memory. Genetically, it feels almost inevitable. My mom’s family has a history of Alzheimer’s disease, while my dad’s family has a history of brain tumors. Both sides also had members who struggled with alcoholism—another indicator of poor brain health in old age.

There’s even evidence for why reflecting on a past self and predicting our future is such a difficult exercise. While it’s relatively easy to recall our past feelings and recognize the differences between then and now, it’s a much larger struggle to project our own futures.

This summer, abandoned by all of my friends for beaches and internships, I found myself alone, lying face-up on the kitchen floor eating Oreos and thinking about the butter wrappers on the ceiling of McElroy...