There is a Buddhist concept called "beginners mind". I think that it is quite a bit like the "optimism" you say you you see in entrepreneurs.

"Beginner's mind is Zen practice in action. It is the mind that is innocent of preconceptions and expectations, judgements and prejudices. Beginner's mind is just present to explore and observe and see "things as-it-is." I think of beginner's mind as the mind that faces life like a small child, full of curiosity and wonder and amazement. "I wonder what this is? I wonder what that is? I wonder what this means?" Without approaching things with a fixed point of view or a prior judgement, just asking "what is it?"

Entrepreneurs with "beginners mind" are able to make their choices and judgements from a much broader palate of ideas. They are not naive, although they sometimes seem it. They don't dwell on what won't or didn't work, they quickly note it, learn from it, and move right on to the next issue... with beginners mind!.