After I graduated business school, I moved to Boston and started my first corporate job working as a salesman for IBM Lotus Development. I lived in a brownstone condo in the South End, and my downstairs neighbor was a wonderful man named Colin O’Neill. He was quiet, humble, and had a thick Northeastern accent. Colin worked in tech, and he helped me figure out how to use the software I was supposed to be selling to companies. After work, we would go for long runs together along the Charles River and, afterwards, we’d earn our calories back by visiting our favorite South End watering hole called The Delux. Before long, he became one of my closest friends.

In the end, I wasn’t cut out for software sales; my dream was to work with kids and help change the world. I sold my condo and moved to Denver to start my own youth leadership non-profit, but I made sure to keep in touch with Colin over the ensuing years. One day he called me to deliver terrible news: He had been diagnosed with stage-four testicular cancer. Colin explained that he had a slight discomfort in his groin that he’d ignored for months until the pain became unbearable. It turned out to be a malignant tumor. Thankfully, Colin pulled through after many rounds of chemotherapy, but the ordeal nearly killed him.

At the time, my dream of changing the world wasn’t exactly going as planned. I couldn’t accept tax-deductible donations because my organization didn’t yet have 501(c)(3) status, so very few people were willing to donate to our cause. I was essentially living in a cot in my office. I could barely pay rent, and I had nearly exhausted all my savings. There were some months when I couldn’t even afford to pay my staff. Every night I’d go to bed thinking: I can’t do this. I’m wasting my time. I’m not good enough to pull this off. I’m not smart enough to change the world.

A few months after I spoke with Colin, just as my life was nearing the breaking point, I began noticing a slight ache in my groin. I tried to put it out of my mind—I had a million things that needed my attention. A few days later it began throbbing, and soon the pain became excruciating. Just like Colin. Please don’t be cancer, I prayed. Please don’t be cancer. But deep in my heart, I knew. 

I booked an appointment with the best urologist in Denver, but the next available appointment wasn’t for two months. The next eight weeks were the worst of my life. The pain was so bad I could barely walk. Using the bathroom was so agonizing that I avoided drinking water. There was no doubt in my mind: I had testicular cancer. I was going to die. I called an attorney and drafted a will. I told my sisters and my parents and my closest friends how much I loved them. I began saying my goodbye’s.

Finally, the day of my appointment arrived. A nurse ushered me into the doctor’s office, and I sat on the examination table. Everything seemed to go numb as I felt the cold metal on my skin. She took a few x-rays and then left me alone. After what seemed like an eternity, the urologist entered. He was a big German man with a thick accent. As he poked and prodded my body, I told him about my friend Colin.

“He has stage-four testicular cancer,” I said. “And his pain wasn’t this bad. Please just give it to me straight: How much time do I have?”

The doctor said nothing as he continued his examination. Finally, he removed his gloves and took a seat next to me. I held back tears as I braced for the worst.

Then the doctor gestured to the corner of the room. “Do you see that bookshelf over there?” he said. It was filled with thick medical textbooks with titles I couldn’t pronounce. “I wrote most of those books. They are used at the top medical schools in the world. Duke. Johns Hopkins. Harvard. I am among the very best in the world at what I do. I tell you this not to brag, but to assure you that the diagnosis I am about to give you is 100 percent correct and unimpeachable.”

Oh god, I thought. Here it comes. My death sentence.

“Mr. Spaulding,” he said slowly. “There is absolutely nothing wrong with you.”

My mouth nearly hit the floor. “What?! That’s impossible. Do you have any idea how much pain I’m in?”

“Your condition is psychosomatic, meaning it’s all in your head. You have been thinking subconsciously about your friend’s condition, and the stress is manifesting itself as pain. Here is what is going to happen. You are going to get up, walk out that door, and then your pain will disappear.”

And then the doctor got up and left.

I got dressed, still somewhat in shock, and followed him out the door. Just as he predicted, the pain disappeared. It was like someone turned off a switch. By the time I reached my car, I felt completely normal. Like nothing had ever happened. 

The entire thing was in my head. I had kept all the stress and anxiety bottled up, and it all had to go somewhere. It was almost as if my subconscious had faked testicular cancer as a cry for help. But then a powerful thing happened. I realized that if my brain could use all those negative thoughts to trick me into thinking I had cancer, what could it do with positive thoughts? For years I had internalized my struggles. I had convinced myself I wasn’t smart enough, that I would never be able to get my nonprofit off the ground. What if instead I simply changed my mindset from “I can’t do this” to “I can do this.” It’s going to be hard, I told myself. There are going to be a million obstacles to overcome. But I can do this.

It worked. Just as I conjured up that pain in my groin, I conjured up the strength to move forward simply by believing it could be done. I finally won that 501(c)(3) status. I worked eighty-hour weeks and crisscrossed the nation for donations. Finally, the money came in. The National Leadership Academy was up and running, and we’ve never looked back since. Next week we are celebrating our twenty-third anniversary in front of hundreds of high school kids whose lives have been changed by our hard-working staff and volunteers. None of this would have happened if I didn’t start believing in the power of positive thinking.

What has your mind prevented you from doing lately? What are those limiting beliefs you have convinced yourself are real? Now allow yourself to think, just for a moment: What if I am wrong?

I may not be nearly as smart as that German urologist. I may not have written dozens of prestigious medical textbooks. But I’m just as confident in my diagnosis: If you have a positive mindset, there is no limit to what you can achieve. You just have to believe.