I've never talked about or really read about it...

but from hearing it, it sorta sounds like what pretty much everyone does for themselves on some level:
- you take care of your own emotional well-being
- you ensure that you're safe
- you comfort yourself
- you ensure you provide yourself with the necessities (and at least some of the wants) for life
- you forgive yourself but hold yourself up to an acceptable standard

I think that's sorta what it could mean? A parent's job is to take care of you physically, mentally, and emotionally. When we're adults, that job is supposed to be transferred to us. They are also supposed to teach us how to interact with others, the difference between right/wrong, what is and is not acceptable behaviour, etc.

I'd think that for many people who did not have sufficient parenting, they either are inefficient themselves at taking care of themselves properly, or they continue looking for someone else to take over that parent-role.

Just my guesses and personal interpretation of it!