As a Buddhist practitioner and a therapist (for lack of a better term), the word "attachment" is packed with irony. Attachment, in the Buddhist sense, is clinging to thoughts, feelings, people, objects, anything that for the moment we invest with a sense of permanence. Suffering arises because nothing is permanent, so we experience loss when we come to depend on something always being a certain way. Non-attachment frees us from how we want the world to be, and allows us to be in the world that actually is.
  In psychology, or at least how I approach it, 'attachment' is the basis for emotional and relational health. The safety and reliability of our earliest caregivers become the foundation for later development. Our inner world of expectations and trust shape subsequent relations with the self, others, and the world.
   One could state that non-attachment in the Buddhist sense is not possible without attachment being achieved in the psychological sense. We need a profound and preverbal confidence in ourselves and the world (and our teacher, I might add) to make that vast leap of letting go.
    The really painful and disorienting miles on the spiritual path can also be seen as a letting go of the failed relationships that betrayed us, and turning our focus to whole of reality, including our experience, and allowing that to be the basis of our (psychological) attachment. From that newfound confidence, we can let go, knowing that letting go is not an abandonment but an acceptance. As Dogen put it, "to carry yourself forward and illuminate the myriad things... is delusion...that the myriad things come forth and illuminate themselves is awakening..." (see this for a helpful discussion of this aspect of Dogen's thought).
  
   The unexpected is the great teacher. When we seek to tighten control over much of our lives, the effort casts a shadow. That shadow is our inability to accept, or even see (!), what we don't expect. The pile of un-lived, unacknowledged life piles up in our darkness, and one day, topples over us.
   In this respect, we deny certain parts of reality because we can't deal with it, because we haven't the confidence (based on prior experience) that we can accept it without being overwhelmed. So it piles up and up, until it can't be denied any longer. But that can go on a long time.