Optimism is basically the same as poor risk assessment. Risk assessment, aka spending time analyzing everything that could go wrong ahead of time. Show me an optimist who does that and I will show you a pessimist.
But the dominant trait at least for serial entrepreneurs might still be pessimism at the core, because it requires willingness to fail. You need to be pessimistic enough to expect to fail many times as a normal course of action until you luck out. If you don't expect to fail then the first large failure becomes the final blow.
This is the same kind of error people make when they assume an introvert must have poor social skills, even though that's often not the case.
There's a meme/comic that goes like this:
Panel 1, "Nothing really matters": a little creature in a void, sad. "What people think nihilism is."
Panel 2, "Nothing really matters": the same creature surrounded by rainbows and puppies, happy. "What nihilism really is."
In the same way that recognizing nothing really matters in our march toward entropy means we can get on with choosing our own path in life, recognizing the pitfalls of a potential path means we can walk it in confidence.
I know there be dragons, and I'm going to date them all.
In my experience people are inaccurately pessimistic, in part due to a lack of imagination. So risk assessment that's more accurate will present as more optimistic.
But the dominant trait at least for serial entrepreneurs might still be pessimism at the core, because it requires willingness to fail. You need to be pessimistic enough to expect to fail many times as a normal course of action until you luck out. If you don't expect to fail then the first large failure becomes the final blow.