For most of my adult life, I believed courage looked a certain way.

I believed it looked like boarding a plane alone to a remote corner of the world. It looked like clipping into a rope at high altitude, pushing forward through fear, and standing on the summit of a mountain that few people would ever attempt to climb.

Over the course of seven years, I traveled to the Seven Summits—the highest peak on each continent. Along the way, I survived an avalanche on Everest, endured brutal storms on Denali, and trekked through some of the most remote places on earth. People often ask me which mountain was the hardest.

The truth is, the bravest person I have ever known never climbed a mountain at all.

She was my mother.

I was twenty-five years old when my mother was diagnosed with ALS. At the time, I was living in New York City, building a career I loved, and imagining a future that stretched out endlessly before me. Then, with a single diagnosis, everything changed.

ALS is a cruel disease. It takes away the body’s ability to function while leaving the mind heartbreakingly intact. Over the next seven years, I watched my mother gradually lose the ability to walk, to dress herself, to eat, and eventually, to speak.

And yet, somehow, she remained the strongest person in every room she entered.

As her illness progressed, I found myself living two seemingly opposite lives. I was climbing mountains around the world while also returning home to care for my mother. One week I might be standing on a glacier in Alaska or trekking through the jungles of Papua. The next, I would be sitting beside my mother at a doctor’s appointment, helping her navigate a world that had become increasingly inaccessible.

For years, I thought these were two separate journeys: one about adventure and achievement, the other about love, responsibility, and loss. I understand now that they were always the same journey.

The mountains taught me many things. They taught me endurance. They taught me humility. They taught me that fear and courage often exist side by side. But my mother taught me what courage actually looks like. It looks like getting out of bed each morning when you know that tomorrow will be harder than today. It looks like choosing gratitude when anger would be easier. It looks like finding reasons to laugh even as your world becomes smaller and smaller. Most of all, it looks like continuing to love the people around you with your whole heart, even while experiencing unimaginable loss yourself.

There is one image of my mother that returns to me often. By the time ALS had taken so much from her, she could no longer do many of the things she had once done effortlessly. Yet whenever I walked into the room, she smiled. Not because she wasn’t afraid. Not because she was pretending everything was okay. But because, even then, she wanted me to know that I was loved.

I climbed thousands of feet above sea level searching for meaning, purpose, and perhaps some understanding of myself. I traveled to the ends of the earth believing that courage was something found in extraordinary places. All the while, the greatest lesson in courage was waiting for me at home.

Now, years after losing my mother, I realize that the most important journeys we take in life are rarely the ones that carry us across continents or to the tops of mountains. They are the journeys that teach us how to love, how to care for one another, and ultimately, how to let go.

I wrote Where the Air Grows Thin because I wanted to tell the story of those parallel journeys: a daughter climbing the highest mountains in the world while learning that the bravest person she would ever know was her mother.

I climbed some of the highest peaks on earth. But if I learned anything from those years, it’s that the bravest journey I ever witnessed wasn’t mine.

It was my mother’s.