As a general rule, I don’t take medicine unless I absolutely have to. I’ve never been one to swallow an aspirin at the first sign of a fever. I don’t seek out antibiotics at the onset of the sniffles. And until recently, I lived by a slogan my high school athletic coach used to say any time students struggled with pain or aching muscles: “Mind over matter.”

But my breast cancer diagnosis in July 2019 taught me that this isn’t necessarily...