Catelyn's anguist at witnessing the death of what she thought her last living son, his wife and her grandchild to be caused her to take an innocent life before having her own throat slit, knowing all the while if she hadn't let the kingslayer go, the ending might be different.
Tis a big and beautiful world. Most of us live and die in the same corner where we were born and never get to see any of it. I don't want to be most of us.