My life up until my illness could be understood as the linear sum of my choices.

Lucy and I met with Emma on Monday. She confirmed the plan we’d envisioned: bronchoscopic
biopsy, look for targetable mutations, otherwise chemo. The real reason I was there, though, was for
her guidance. I told her I was taking leave from neurosurgery.
“Okay,” she said. “That’s fine. You can stop neurosurgery if, say, you want to focus on something
that matters more to you. But not because you are sick. You aren’t any sicker than you were a week
ago. This is a bump in the road, but you can keep your current trajectory. Neurosurgery was important
to you.”
Once again, I had traversed the line from doctor to patient, from actor to acted upon, from
subject to direct object. My life up until my illness could be understood as the linear sum of my
choices.
what is this part"My life up until my illness could be understood as the linear sum of my
choices." means? thanks in advance