The risks can be learned about and the fear of them relieved.
I agree, the idealizing does come from being in our heads too much: idealizing is deciding that a person is a certain way based on our own thoughts and not on the reality of that person, so that is certainly in our heads.

Being in our heads seems like a safe place to be, when the world seems too frightening. On one level it makes perfect sense to protect ourselves that way! But on another level, it isolates us from the very thing we want: closeness with others and the more comforting safety in that.