If you grew up in an emotionally unstable environment, you would have learned to watch for any little thing that might set them off. You learn to do things perfectly to avoid being shouted at or punished. You learn to watch facial expressions and subtle changes in the tone of voice. We learn these as children to stay safe. To stay safe, we became vigilant. As adults, there is still this little child within, part of our subconscious, terrified of being abandoned or hurt again. So the little child within will keep watch. Will be vigilant. Even when everything is safe, they will be keeping watch.