Strong boundaries are not walls.
They are like good fences, as in “Good fences make good neighbors.” Good fences keep people from wandering into your backyard unless you invite them. Good fences have a gate that you can open up any time you want, but only when you want.
Having strong boundaries means that you are able to protect your peace. It means being able to say no, and never being pushed beyond what you are comfortable with unless you decide that is where you want to go. Strong boundaries help you clearly define which are your own thoughts, feelings, and beliefs and which belong to others.
Boundaries help you feel safer, and therefore more open, because you remain in control of your own space.