Attachment Theory
The idea that early bonds with caregivers shape how comfortable someone is with closeness and trust in relationships throughout life.
Attachment theory started with psychiatrist John Bowlby's work in the 1950s-60s, arguing that infants have a built-in need to stay close to a caregiver for safety, and that how consistently that need gets met shapes later relationship patterns.
Researchers later extended the same framework to adult romantic relationships, which is where the 4 attachment styles, secure, anxious-preoccupied, dismissive-avoidant, and fearful-avoidant, this site's attachment style test measures come from.