Some people seem to never learn - I'm convinced because they do not have well developed 'self listening skills'.

"what gets in her way the most is her telling herself she's stupid and harmony-challenged and will never get it. As soon as she shifts into the "just working it out" phase and starts to listen to the notes instead of her own self-deprecation"

I knew someone who was told by her school 'music teacher' that she would never be able to sing. This teacher was obviously useless as a music teacher (wonder how many other kids she stuffed up?) - as soon as I showed this lady how to LISTEN to herself, she began to realise how off key she really was, and began to rapidly improve within weeks.