Please help me understand self-loathing and low self-esteem

This might be a sensitive subject for many.

Please do not take the following question as a personal  judgement, I am honestly trying to understand so that I can try to improve my empathy and compassion, and possibly find ways to help people along the way. I also get it if it isn't something you're happy to talk about.

It seems there are many people out there, and on this forum, suffering from low self esteem and self loathing.

Where does this come from?

Does it come from:

• poor self image
• bullying
• general anxiety and depression
• external criticism
• lack of achievement
• isolation
• being overwhelmed by the senses

I am genuinely interested, as it's something I don't think I have ever experienced.

I'm sure I have had anxiety at times, but I'm not really able to to apply names to feelings, so I don't really know. My partner has said that I can be emotionally insensitive because I try to rationalise everything. But I have also been told that my blunt, rational, and sometimes cynical approach has been helpful at cutting through the noise.

Although I've been bullied, embarrassed, ostracised at times, although life has been difficult, and I can be self critical and insecure, I don't think I've ever felt loathing or worthlessness.

Maybe it's because I'm very insular in my thinking, that I haven't paid too much attention to the real world, and therefore shrugged off much of the sh*t that's thrown at me. 

Again, I'm genuinely interested as I would like to understand people better so that I can help people better. But this part of the emotional spectrum is truly a foreign land to me.

I find it sad that so many people are suffering in this way, and like to understand why it is.

Thanks.