At the turn of the millennium, Alger, an investment management firm, was thriving. We had the top-performing fund of the internet era and were growing significantly. Just a few years prior, we had moved into a new office on the 93rd floor of the World Trade Center's North Tower. The office was a great source of pride for our firm and for our CEO and CIO, David Alger. It reflected how far we had come in the 30 or so years since his brother founded the firm.

In the early years of the internet, one of our analysts took a photo from a 93rd floor window overlooking the Statue of Liberty and New York Harbor and posted it online with a personal note: "Freedom! Liberty! The ultimate symbol of the greatest city in the world."

Thirty-five of Alger's beloved employees, including David, were lost in that office on Sept. 11, 2001. They were the heart of our investment team and leadership.

I was one of only surviving four members of our World Trade Center team. I was at a meeting in Midtown Manhattan that morning. Another survivor, Patrick Kelly, then my young research associate and now one of our portfolio managers, was lucky enough to be in at an investment conference in California.

When I walked out onto 42nd Street after my meeting that day, I noticed traffic had stopped. People were standing in the street, looking southward down Lexington Avenue and toward downtown. We could see smoke rising. I don't know how long we stood there. When the Twin Towers collapsed, the view of downtown disappeared behind a cloud of smoke and debris.

Alger lost much more than 35 investors. We lost 35 mothers, fathers, daughters, sons, friends, and loved ones who made up the fabric of our firm. So I wasn't surprised that many Wall Street insiders, consultants, and industry observers were more or less certain Alger could not and would not survive our losses. We would go out of business or perhaps continue but in a diminished form, profoundly changed and never again a relevant, much less a leading, investment management firm.

Some had similar predictions for New York City as a whole. Life here would be too risky. People would leave. The city would lose its pull on the ambitious people who had always been drawn here.

They were wrong on both counts.

Alger was determined to rebuild as Alger. Some advised me to hire star portfolio managers and their teams from other firms, but I rejected that approach. To honor the legacy of the firm and the colleagues we lost, I believed we had to rebuild around our existing investment process, philosophy, and culture.

Fred Alger, the firm's retired founder, helped us regain our footing in the immediate aftermath. Several former Alger portfolio managers came back to the firm. We then hired and trained a new generation of analysts to identify and invest in high-growth companies undergoing transformation, which Fred called "Positive Dynamic Change." Today, we manage more than $47 billion in assets, and the values and contributions of the colleagues we lost remain part of who we are.

New York didn't fade either. Google and Salesforce established major offices here in the immediate years following 9/11. Other New York firms expanded their footprint. Tens of billions of public and private dollars were spent on rebuilding. The city's fundamental appeal as a place to build, create, and compete endured.

Markets have undergone their own remarkable transformation. In 2001, we were still in the fog of the dot-com bubble, with investors trying to understand what the internet would ultimately mean for business and the economy. We are now asking many of the same questions about artificial intelligence. Investing through both of these unsettling periods has reinforced for me that moments of great uncertainty can also be moments of extraordinary innovation and opportunity.

Worry has a tendency to compound: It can become easier to imagine how things might get worse than how they might get better. Still, I believe that we are in one of the most exciting, transformational eras of investing we may see in our lifetimes.

That isn't to say all is well in the world. There is no shortage of reasons for concern about markets, the economy, geopolitics, and the world more broadly.

But this week, as I do every September, I am reflecting on what is right and good in it. The past 25 years have taught me that resilience isn't simply the ability to withstand adversity. It is the ability to move forward without losing sight of who you are or what you believe in. That was true for Alger. It was true for New York, and I believe it remains true today.

Guest commentaries like this one are written by authors outside the Barron's newsroom. They reflect the perspective and opinions of the authors. Submit feedback and commentary pitches to ideas@barrons.com.

Dan Chung is chief executive officer, chief investment officer, and portfolio manager of several strategies at Alger.