Like an onion, boundaries have layers. Many layers. In fact, they can have as many layers as you want, because they're yours. However, if like me you were raised to believe that protecting yourself if selfish and therefore wrong, you're probably very new to the concept of boundaries. The word "No", as painful as it may be to use at first, will become your weapon of choice when defending your personal boundaries. You're not doing anything wrong by protecting yourself.