After dealing with friends who have this issue, it comes down to self esteem. They might even develop a pseudo-stockholm syndrome and start liking the people who insult them, relying on them for validation. this is the worst possible thing to happen. Doubts can surface from yourself, but they mostly surface from fear of judgement of others. If people continuously insult or hurt someone, they could develop depression and lose all self esteem and even start insulting themselves.
How can you help someone with depression or low self-esteem?
You can help by letting the person know that you are there, and try your hardest to get that person away from the crowd that insults her. Even if the only alternative is isolation or cutting ties with nearly all of their friends, it is the only way to help them get back on track. They may even get happier and stop insulting themselves. You can't force someone into doing this, however. Any time they bring up an insult that someone gave them, remind them to stop hanging around them, and tell them that continuing to associate with them will only bring more pain and insults. It is always hard to help someone, and sometimes the best you can do is just stick with them. dont let them down.