Daf Dubbelman is a real estate entrepreneur, endurance athlete, and Harvard Business School OPM participant who is completing the program for the second time. Daf shares the mindset that drives both his athletic and business pursuits: start before you feel ready, challenge conventional limits, and always ask, “What’s the worst that can happen?”

Through stories of running marathons in places like Iran and North Korea, preparing for 226-km Ironman races, and even registering for a 600-km Sahara cycling challenge, Daf explains how endurance sports shape his approach to leadership and entrepreneurship. For him, the real victory is not winning but showing up, finishing, and pushing past mental barriers.

He also reflects on lessons from Harvard’s OPM program, emphasizing the power of relationships, cross-cultural experiences, and learning from failure. Ultimately, Daf’s philosophy centers on embracing discomfort, redefining success on your own terms, and influencing others through example, whether that’s tackling extreme challenges, negotiating in business, or encouraging healthier, more sustainable habits.

Here are the Top 10 Takeaways from the conversation:

1. Ask: “What’s the worst that can happen?” Daf’s core mental model is simple: most fears collapse when you examine the downside. In endurance sports or business, the worst outcome is often trying and not finishing, which is still far better than never starting.

2. The biggest risk is not starting. He believes the highest probability of failure comes from never entering the race, whether that race is an Ironman, a marathon, or a business venture.

3. Finishing matters more than winning. Completing a challenge is often what people remember. Daf notes that no one asks your Ironman time, they simply recognize you as someone who finished.

4. Most limits are mental, not physical. With focused training and determination, Daf went from barely swimming to completing a 3.8-km Ironman swim in just a few months, proving that mindset often matters more than initial ability.

5. Turn competition into personal challenge. Rather than competing with elite athletes training 30 hours a week, Daf encourages people to define their own race and measure success against their own goals and constraints.

6. Create your own peer group. Success becomes more meaningful when you compare yourself with peers who share similar realities, such as entrepreneurs balancing business responsibilities with training.

7. Extreme experiences expand perspective. Running marathons in countries like Iran and North Korea exposed Daf to cultures often misunderstood in the media, reminding him that direct experience breaks down assumptions.

8. Endurance sport mirrors entrepreneurship. Both involve setbacks, uncertainty, and repeated attempts. Just like in a race, business success often requires pushing through pain, adapting, and trying again.

9. Celebrate milestones instead of endlessly chasing the next goal. Daf believes leaders should set targets, reach them, and celebrate with their teams rather than constantly moving the finish line.

10. Invest in relationships and learning. For Daf, the greatest value of the Harvard OPM program isn’t only academic content, it’s the global network, shared experiences, and lifelong friendships that come from learning alongside diverse leaders.

What’s the Worst That Can Happen? Running Marathons in Iran and North Korea - Daf Dubbelman