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I jogged into the Stanford Cancer Clinic with my boyfriend, the youngest people there by two decades. We stood there sweating and holding hands, a jarring sight in the sickly light.

“You are 18, right?” the receptionist asked. Behind me, a woman so gaunt that her cheekbones protruded rolled by in a wheelchair. The oncologist called me alone to the exam room, and I told her the story I had revealed to more doctors than friends: I carry the BRCA1 mutation, which gives you a 98 percent chance of developing cancer.

When my family found out that I might have inherited the mutation from my mother, we took it as a given that I would get tested. Scientists, atheists and lawyers, we are compulsively rational. Yet when I learned I carried the mutation, I felt the cruel weight of a paradox: you can never know whether you want to know until you already do.

At Stanford, I study artificial intelligence, in which math is used to resolve these sorts of dilemmas. My teachers claim that gaining information never hurts. It can be proved mathematically that a robot with more information never makes worse decisions But we are not robots. Our eyes don’t filigree the world with coordinates and probabilities, and they can be blinded by tears.

Still, we, too, display a preference for information. We dislike uncertainty so strongly that we sometimes even prefer bad news. One study of people at risk for a terminal disease found that those who learned they were going to die from it were happier a year later than those who remained uncertain about their fates. Most people have a deep intuition that a life lived cleareyed has inherent value, independent of whether the truth makes you happy. But surely this has limits.

I know there are some things I do not want to know: which other girls my boyfriend finds attractive or the day and manner of my death. The truth can hurt in two ways. It can worsen your options: you can’t live as happily with a significant other after learning of his infidelity. Or it can make you irrational: hearing about terrorists targeting airplanes may lead you to drive instead of fly, though planes remain much safer than cars.

So was I wrong to unwind my double helix?

My risks of getting cancer at 21 are too low for me to do anything differently to better my odds. The knowledge is both irrelevant and painful; it’s obsessed me and made me behave irrationally. I wake from nightmares in which I am dying from cancer. I reread the memoirs of patients with metastatic disease until I can’t see the text through my tears. In my supposedly rational pursuit of knowledge, I’ve gone a little mad.

Despite an excess of information, I pursued more, enrolling in Stanford’s cancer biology class. The professor filled his slides with dark oncological puns, lecturing with the almost robotic detachment I sometimes see in those who work closely with cancer. Maybe I, too, am becoming robotic. I can laugh at the puns, calmly press lecturers on survival rates for breast cancer, marvel at the elegant molecular mechanisms by which it eats us alive. Just as tumors eventually swell too large for their hosts to endure, will all this knowledge grow past what I can handle?

The prospect was too much for my mother, a far tougher woman than I am. When she received a diagnosis of breast cancer, she ordered the doctors to give her chemotherapy as rapidly as possible and recovered completely. But she refused to learn her chances of long-term survival or look at her medical records. I became the first in my family to read them, and when I learned her cancer had been unusually lethal, my father asked me not to tell her.

I cannot shake the thought that this mutation was given to me for a reason. I don’t believe in God. I know my chromosomes divided along a random schism, not a divine skein. But while I reject the theist’s idea of God-granted purpose, I accept the existentialist’s idea of crafting your own. The world may be only sound and fury, but we can choose to see patterns in that chaos, stories in the stars.

So I choose to believe that I have been given this mutation so that I can discover how to overcome it. Like the protagonist in “Flowers for Algernon,” I will be both scientist and patient. Even if this sense of purpose is illusory, it lets me do what I couldn’t before. Fear has sharpened me: I wake at 3 in the morning to refine biological algorithms or to read papers on ovarian cancer.

While I believe this knowledge has made me live better, I am not sure it’s made me happier. True, there was the day I dropped by Stanford’s Relay for Life, a fund-raiser for cancer research, ran farther than I ever had and walked home full of joyful purpose. There was also the night I lost it completely and sobbed for hours in my boyfriend’s arms.

In this oscillation between light and dark, one thing remains constant: I’m no longer so eager to illuminate my fate. Recently, I went to the Web site of 23andMe, a company that will read from your genome your risk of dying from a hundred diseases. I clicked through the testimonials and was unnerved by how similar our reasons were for wanting information. I looked down at my fingertips, tempted: what else in my genome waits to be found?

But then I clicked away. The Bible doesn’t tell us if Eve ate any more apples, but I have had my fill of revelations. I am 21 years old, and I want to be free to live a normal life: fate unbound by double helix, future exploding with possibility. I don’t want to know.