Most people want to believe their parents are good people and were good parents to them. To keep this belief is to keep your world stable and good. If your parents were normal people they made mistakes that have affected you. Some parents are so injured themselves that they, for the most part, weren’t good parents at all. Some parents are downright destructive and their children are lucky ( or marvelously resilient) to come out of their childhood relatively intact. Some children don’t.
The truth is there are no perfect parents. There really aren’t. People not willing or able to see their parents’ limitations and mistakes lose out in understanding and forgiving themselves for their own limitations, and often feel bad about themselves. They make excuses for their parents, seeing them so much as victims of their own situations and therefore not ultimately responsible for what they did – or didn’t do – to their own children. So the adult child inwardly makes themselves bad to protect the parent from responsibility for their own behavior. For these people the parent must remain good, or at least not as faulted/limited as they were. When in therapy, these adults lose out on what they might learned about who they are and why they are the way they are. They can’t overcome the mistakes or cruelties from their parents; you can’t fix something that didn’t happen. And you can’t find out what did happen if you aren’t willing to be open to what you find when you look.
People who protect their parents and lose out for themselves are often relying on the parents to make them feel OK, instead of taking it on themselves to make themselves feel OK. This is a growing up process that many times people resist. Of course we all want our parents to love us, but if they screwed up and our self esteem is lower than it could / should be, it’s time to take on the work of finding out how to validate and love yourself. That’s therapy.