What we encounter (the process/therapist) are like concrete. The things we want to become like clay are normally outside of us, hence at times one may think it is the things outside of us that need to change, when in reality, it is what is inside of us that needs to change.
So, when concrete (long term styles of thinking, acting, viewing the world) meet the therapy process (boundaries)that are firm...something eventually gives way. A certain way of looking at things can be changed if we are willing to realize you can't keep running into a boundary without there being some sort of encounter with what is within us vs. what is outside of us.
There are certain themes that one encounters while in therapy that no matter how much we hope or wish, they do not change. How many times before running into the same cement wall does one become pliable?
There are things within us that are concrete that must be transformed into something more pliable and the concrete process of therapy can help with accomplishing this, although it is painful and very difficult.