It opens your chest and it opens your heart and it means someone can get inside you and mess you up. You build up these defenses. You give them a piece of you. They don't ask for it. They do something like kiss you, or smile at you, and then your life isn't your own anymore.
Love takes hostages.
It gets inside you. It eats you out and leaves you crying in the darkness, so a simple 'maybe we should just be friends' or 'how perceptive' turns into a glass splinter working its way into your heart. Not just in the imagination. Not just in the mind. Nothing should be able to do that.