My tuppence-worth on this, I'll try and keep it brief. I used to be a Samaritans listening volunteer. Some of the people I spoke to had horrible lives from day dot, and had really disordered thought patterns and attitudes. Not their fault. Anyway, I would wonder afterwards just what it would take to help one of those people escape the chaotic, miserable patterns they were in. I felt it was theoretically possible, but the huge resources it would take makes it practically impossible - I felt like it would take years and years of intensive intervention from a whole range of professionals: psychiatrists, therapists, doctors, teachers/educators, job coaches, plus removing them from their old life completely somehow.
I was also quite naive, but listening to those people helped me see just how complicated some people's lives are. No easy fixes.
It's interesting to hear people's thoughts here about personality disorders and how that might impact someone's ability to change. It reminded me of the Samaritans callers - maybe it's theoretically possible, but practically impossible.