That we shut down is not the problem. In fact, to become aware of when we do so is an important part of mind training. The first step in cultivating loving-kindness is to see when we are erecting barriers between ourselves and others. Unless we understand, in a non-judgmental way, that we are hardening our hearts, there is no possibility of dissolving that armor. Without dissolving the armor, the loving-kindness of bodhicitta is always held back. We are always obstructing our innate capacity to love without an agenda.