When thinking about the character traits useful for starting a company or bringing any kind of creative idea to life, two traits seem important: confidence and resilience.
I used to think that confidence and faith in your ideas were what mattered most. You need to have the ability to spread excitement for the thing you are working on to convince investors, customers, and your team. For this, confidence seems to be the important trait.
Although confidence matters, I came to realize that resilience matters more. No matter how confident you are, if you give up easily once things get tough, everything else cancels out to zero. One determinant for startup success is the ability for people to not quit. The simple fact that you figure out how to not run out of cash and continue to live increases the likelihood of success for your company significantly.
If resilience matters more than confidence, how can we test for that as investors betting on people? Unfortunately, it's hard. Testing for confidence is easy. You see it in the way someone speaks about their ideas and the way they are present. But resilience is tricky.
The best proxy I have found for the degree of resilience of founders is trusting my gut feeling. It's an unsatisfying answer, yet the only one I know of. Perhaps one also needs to accept the fact that this is the error term in investment decisions, the unknown risk.
Yet, the awareness that resilience matters more than confidence alone is already useful in itself to understand the likelihood of success of founders more accurately.