There's a tryout period, of course. We figure out pretty quickly what kind of father we have, if he's around. And we figure out how the kind of father we have influences the kind of mother we have. As infants, we learn—though we don't have the words for it—that damaged fathers often seem to couple with damaged mothers. That damage can look like narcissism, depression, anger, anxiety, addiction, abusiveness, paranoia, withdrawal, and all manner of "abnormal" behavior. Of course, we grow up seeing it as normal. What do we know? "Normality" is by definition what we get a lot of. We don't have to be statisticians to understand that. Rare respites from chaos, danger, confusion, and despair, are merely outliers on our unconscious home life tables and graphs.
Fast-forward to adulthood and the residual coping mechanisms (sometimes called "brain chemistry imbalances") are no longer applicable. Whether we have left that toxic world behind or are still enmeshed in it, the attitudes and behaviors we developed under false pretenses are not at all useful—if they ever were. Our mistrust, hypervigilence, avoidance, isolation, defensiveness, aggression, dissociation, or whatever is out of place once we are out of that place. As adults, the dad who wasn't there, or shouldn't have been, often hangs around (just as the wonderful ones do). He is inside us. Being aware of that is the first step in processing his residue.
And here we sit, left to pick up the pieces the best we can. Since we group members have each other, "the best we can" is better than it might otherwise be. Together, we move on to Step Two. After awareness of the residue, what it means to us, what we "normally" do with it, how it affects us—consciously and unconsciously—and how it persists, after all this awareness comes the decision to think, feel, and behave more like we'd like to. This decision is a big step. It's not easy, but it's simple. We just try and do it. Little by little. A bit at a time. We choose to act "as if" we've already sorted these matters out, already processed, or already forgiven.
Then I grew up. I changed the rules. With help. I decided what would make me proud. And observing healthier boundaries was something that gave me my own sense of pride. And I tried to become the kind of father I would have wanted. It's taken a long time to make the transition from shameful son to proud parent. It hasn't been easy, and I'm not finished. I'm making progress. Just like the other good people I know who are earnestly sorting this stuff out. It helps that we're doing it together.