The year my youngest son, Aidan, graduated from high school, I was asked by his graduating class to deliver their commencement address. The talk I shared was a bit peculiar. At one point, I’m sure the audience felt they were listening to the world’s worst graduation speech.

“Congratulations, graduating class of 2019!” I started on an upbeat note. So far, so good! I dutifully recognized the parents and grandparents. I thanked the faculty, staff, and administration of the school. All the normal things you say. That done, I took the talk in an unexpected direction.

“Graduates, in commencement speeches, you expect to hear something like this: ‘You can be anything you want to be. Do anything you want to do. Aim high. Shoot for the stars. Follow your dreams!’ But that is not what I am going to say. Because psychological research tells us that we’re pretty awful at choosing what will make us happy. So here is my advice, class of 2019: do not follow your dreams.”

I will admit I was exaggerating to make a point. But I wasn’t too far from the truth. Psychological research has shown that we struggle in choosing the things that will make us happy. You’ve experienced this, choices large and small that didn’t bring you the satisfaction or joy you had hoped for. You follow your dreams only to feel a bit let down in the end. Or arrive with a sense of regret. You climb the mountain, survey the summit, and ask, “I worked so hard, I sacrificed everything, for this?”

But the deeper point I wanted to make to the graduates wasn’t that we struggle to make good choices. My deeper point was that even if the compass of our life were perfectly pointed toward happiness, few of us make it safely to that far shore of joy. Life gets interrupted. You took a detour, and it became the destination. Life had other plans for you. Even if your dreams point toward happiness, dreams can be broken or unfulfilled. Think back to your high school graduation, when you were told to follow your dreams. How’d that work out? Have your dreams become reality?

Life teaches you pretty quickly that dreams are fragile things.

“Few of us go from win to win in life,” I said to the graduating seniors. “Maybe a lucky few of you will never face a disappointment. Never get sidetracked or lost. Perhaps you will achieve every goal you set for yourself. But the rest of us? Life isn’t so easy. We get fired from jobs. We get divorced. Our phones ring with news of a diagnosis or an accident.”

Looking back on this speech now, I sympathize with that poor audience. But at this dark moment, I made my final turn.

“Class of 2019, I’m not interested in the best day of your life, the day your dreams come true. That’ll be an amazing day. You won’t be looking around for help on the best day of your life. But we will also face some hard times and dark nights. Things won’t go the way we planned. Our dreams will get broken or won’t be all we had wished for.

“And so, graduates, I’m not concerned about your best day. The good days will take care of themselves. What interests me now is your worst day. Which brings me to the question I came here to ask you: Class of 2019, how are you going to face the worst day of your life? What will get you through your lowest point and darkest moment, when you experience heartbreak, failure, shame, and regret? Who will you be when you are holding the shattered pieces of a broken dream? How do you survive that day?”

I’m sharing my graduation speech with you to ask you the same question. What is going to happen when you arrive at your lowest point? How will you face the worst day of your life? If life is a final exam, this is the only question on the test. And everything depends on your answer.

Despite every graduation speech you’ve ever heard, following your dreams isn’t the secret to happiness. Joy isn’t ultimately found on your best day. Life is glorious when your dreams come true. The urgent, pressing question is how we face our worst days. The secret to happiness is found in the darkness.

That secret is both simple and surprising, and it boils down to psychological geometry. Joy has a shape.

Look around. The world is in pain. Mental anguish is an epidemic. Consider a new type of death we’ve started tracking. Never a good sign when you have to insert a new column in your spreadsheet tracking mortality statistics. Called “deaths of despair,” these are deaths due to suicide, drug overdose, or liver disease from chronic alcoholism. Average life expectancies have been declining in the United States because of a sharp uptick of deaths of despair, in some demographic groups by over 300 percent. And this is just one small piece of our much larger mental health crisis. Rates of mental illness, from depression to anxiety, are rising with each new generation. And everyone, regardless of age, experiences chronic vulnerability to what some psychologists have called derailment, the precariousness of happiness given how our dreams and best-laid plans can be so easily knocked off course. Life is chugging along smoothly right up to the moment when the train crashes and is thrown off the railroad tracks.

Our modern vulnerabilities to both despair and derailment can be traced back to a radical change in the geometry of the self, a slow development that has happened over the last five hundred years. As the philosopher Charles Taylor has described, the self was once curved outward. Psychological stability was achieved by making contact with a transcendent, spiritual reality that existed outside and beyond the anxious drama of our inner lives. But over the last few centuries, as Taylor recounts, our mental life has slowly become curved inward upon itself. The modern ego is self-absorbed. We’ve become trapped within ourselves. Our struggles with both despair and derailment have emerged because of this fundamental change in the geometry of our lives. Are you curved inward upon yourself? Or are you curved outward, reaching out to connect with a transcendent, sacred reality that exists beyond yourself? On the morning of the worst day of your life, your joy will be determined by this, the shape of your soul. Geometry will determine your destiny.

This is an excerpt from the introduction of The Shape of Joy.