- Actual domain expertise (a summer internship or talking to a few people doesn't count)
- A solid grasp on business fundamentals and managing teams effectively
- A strong network of people who serve as potential employees, partners, customers, mentors, etc. due to being outgoing and generally spending time on developing relationships
- An uncanny ability to recognize niche business problems that are underserved by existing options
- A willingness to laugh at concepts like "work-life balance", "happy marriage", and "spend more time with your kids"
- The ability to build a strong team from nothing and keep it strong by firing people who suck and rewarding people who are good
- Recognition of what you are and are not good at, and then finding good people to do the latter for you
- The ability to sell things effectively (no, if you build it they probably won't just come)
I'm sure others on HN have their own lists.