From an attachment perspective, the anxiously-attached partner is the product of their historical watchfulness - a behavior necessary to ensure the child's safety and survival in the face of uncertainty. The avoidant partner, on the other hand, had a self-sufficiency forced upon them. Attachment theory is very helpful in addressing the lived experience of the couple. 

From a structural perspective, however, anxiety arises when we lose the fantasy that tells us who we are in the eyes of the other person. When a partner pulls away, the anxious partner doesn’t just feel abandoned—they fall into a gap where their place in the Other’s desire disappears. And when a partner comes too close, the avoidant partner isn’t simply overwhelmed; they feel the Other’s desire pressing too insistently, threatening to define them. Anxiety appears whenever fantasy slips, and we find ourselves suddenly too far from the Other, or far too close. 

Attachment theory describes the emotional weather of a relationship. The structural view describes the architecture beneath it. Both perspectives are powerful ways of understanding a couple.