I have come up with a new twist on an old saying:
Fool me once,
Shame on you,
Fool me twice,
Shame on me,
Fool me thrice,
We give family members, particularly our children, second and third chances. We are willing to sacrifice for their benefit because they are extensions of ourselves. Fool me thrice, you're part of me, you belong to me.
Where do we draw the line? When their misbehavior risks the well-being of our other family members, especially the youngest. Consider sloughing any relationships which do not benefit your progeny, directly or indirectly. Cull without hesitation any that threaten.