1. Were determined.
2. Demonstrated perseverance.
3. Suffered rejection.
4. Are adaptable.
5. Weren't motivated entirely by money.
The primary reason a founder succeeds is that he or she works on the right thing at the right time and does it in the right way. That's vague and practically unactionable, so it's not going to become a popular view, but the reality is there's no set of character traits that guarantee success, and there's no blueprint for building a successful company. If there was, 90% of the founders in Silicon Valley would be fabulously wealthy, and half the people who attend Startup School would have a unicorn within two years.
You can have incredible character traits, but if you're working on the wrong thing, or going about building the right thing at the wrong time in the wrong ways, it doesn't matter how smart, hard-working, adaptable, etc. you are.
The power law distributions at even the best venture capital funds demonstrate just how difficult it is to identify founders who are going to succeed, even when trying to do so is your full-time job.