I much prefer the term "social phobia" (implying a learned fear) over "social anxiety disorder" (implying some genetic issue causing excessive fear/inhibition around people). They may well coexist, though. The core issues with AvPD seem to my mind, to be expectations of social failure, very negative self-image, and behavioral avoidance of risk (especially social risk). Withdrawal into fantasizing/planning over useful action and other ineffective but "safe" attempts to feel more socially acceptable or important are other likely factors, from what I have read.

Based on (unofficial) tests, observation and therapy, I seem to have moderate social phobia and SOME Avoidant personality features, which never developed into a personality disorder (I am very grateful for that!) I notice I have evident "triggers" for the assumptions/behaviors that remind me of AvPD.

I find the concept of "Schema Theory" really interesting. It theorizes that common learned fears can become enmeshed in a set of negative assumptions, and then cause self-defeating behaviors based on those assumptions. It's like CBT except for stronger emphasis on deciphering the events which caused, essentially, a fear of powerful and valid psychological needs not being met. Schemas, amplified to the strongest degrees, seem like a potential catalyst for personality disorders. One can have schemas, but never develop a personality disorder. Think of someone with abandonment fears causing a degree of situational difficulty, versus someone with all the features of Borderline, for example.