Parents just don't understand

I just watch Silver Linings Playbook. It was not what I expected. Basically it was two people suffering from PTSD fall in love and how their families have to deal with them. There's a moment in the movie that really spoke to me since my family is dealing with the same issue. Robert De Niro plays the father of the son who suffers PTSD and Bipolar after he discovers his wife having sex in the shower with another man.
After several incidents, including fist fighting with his son for hitting his wife, the father sits down with his son and confesses to not spending enough time with him. He then says he didn't know how to handle his son.
I can imagine this happening to lot of parents. When a child grows up with a mental illness that isn't detected and then one day as an adult that child breaks down and depends on you once again, its gotta be difficult to understand. From my personal experience it is impossible to do anything about it.
I think the hardest thing to accept for a father in this situation is that you messed up. Of course no one will tell you this. Everyone believes that raising kids is a crap shoot. You pick your favorite and hope for the best for the rest of them. But when there is child who seem to fail at life, part of that failure ( if not all because the child has your genes) is your fault.
I'm starting to believe this because of a book I'm reading "The Seven Habits of Highly Effective People." The first part of the book explains the need to balance your relationships with work and success. For example if you never talk with your child and listen to his needs, then as an adult your child will not talk to you.
In my experience I find my father wanting to become friends with me in my adult life. I think this is mainly due to fact that he is alone now with my mentally ill brother who doesn't talk to anyone. It's hard for me to even think of conserving with my father as another regular person or even friend. There's just too much emotional restraint. We never had an open dialogue in my childhood. It was do as I say or face punishment. I still have that same sense as an adult. I don't believe that a joke would go very well with my father. Nor could I see us watching a game together. There is nothing more scary then knowing that you have sowed a bad seed.