I think it's a combination of everything. IMO ET can stem from adult feelings based on the here and now but also stem from needs not met/feelings that occurred in childhood years, usually a preverbal time period when a child wasn't able to use words to describe their needs. The paternal part is often there too partly from childhood stuff and partly because here you are sitting in a room with someone whose job it is to help you. I.e take care of you in different ways. That kind of environment is likely to evoke paternal/maternal feelings especially in those whose needs weren't met as a childhood. These are just some of my thoughts on it obviously may or may not have any truth to them so take with a pinch of salt.