These are broad generalizations about human beings and, of course, there are major individual differences and, yes, not just your personality but your emotional history matter. Interestingly enough, people who are raised in loving and attuned environments ( the securely attached) may be more vulnerable to the persuasions of optimism than those who were not. The study I cited about depressed individuals being more realistic about agency than those who were healthier overall and optimistic has been a hot button of discussion, but it still illustrates the fact that unbridled optimism isn't always an ally. Certain endeavors —like starting something from scratch—are benefitted by large doses of optimism but then, along the way, when you have to assess whether the something you've started is working, you need to be able to tamp that enthusiasm and put on a different hat.
Does that help to explain it?