I had a pretty non-existent self image at least consciously. I always found it really weird when people would talk about the kind of internal dialogue they have going on surrounding self image. Realistically I have a negative self image but I don't really identify with the self loathing part so people always assume it's great. For example I've never connected with those girls who always have to have their make up done or freak out over a less than perfect picture yet my self esteem isn't really that much higher than theirs. I don't have much confidence in groups but I've never actually consciously avoided them. I have crazy problems with self doubt but I step into roles all the time that I normally doubt myself over. I've gathered that I'm like this because although I have a crappy self-image I'm very disconnected from my self and therefore self-image. I remember being bullied for a short amount of time when I was younger, at the time it never seemed like it bothered me so I decided that maybe I just didn't have the attention span for this. Even the bullying that did bother me didn't bother me in a conscious way. Like other people would think "I'm going to avoid this situation" where as I'm pretty sure if it was a cube that shocked me I would keep picking it up. The mind is freakishly capable at protecting us.
Yes and no. From what I gather if the skill is developed it requires some brutal shit to squash it but if you never developed the skill in the first place due to not having certain things from the get go that will do it as well. Certain things need to be nurtured in the early months and years so having caretakers who are emotionally neglectful early on leads to children who don't really process those emotions properly.