Attachment theory started with the work of John Bowlby and Mary Ainsworth, and the basic idea is simple enough. The care you got early on teaches you what to expect from closeness: whether people stay, whether it is safe to need something, whether you will be a nuisance if you ask. Inconsistent care, loss, a parent who was there but not really there, trauma, or a later relationship that went badly can all shape those expectations. None of it fixes your future. It just sets a default you never consciously chose.
Attachment styles are usually described in four broad patterns. Most people recognise bits of themselves in more than one, and the pattern can shift depending on who you are with.
In close relationships this can show up as difficulty trusting people, sharp conflict over small things, going cold, over-explaining, or low self-esteem that quietly runs the whole show.
Worth being clear about one thing. Insecure attachment patterns in adults are not the same as a diagnosed attachment disorder. Reactive attachment disorder and disinhibited social engagement disorder are specific diagnoses defined in childhood in classifications such as the WHO's ICD, and they are not something to conclude about yourself from a quiz online. A therapist can help you make sense of what is actually going on rather than fitting yourself to a label.