Imagine yourself in a room surrounded by four walls. These walls are impenetrable, and nothing can get to you inside this room. Nothing. However, if you knock down one of the walls, then you allow things to enter into the room.
Many of us live an existence that does not allow happiness to enter into our state of being. We make the error of thinking that we must pursue happiness. Actually, happiness is all around us. It is only when we knock down our own mental walls and let happiness come into our being will we obtain it.