Why do some people make choices they KNOW will cause extreme pain?

Explanation: If I know that a specific choice will cause pain to myself or someone else (not maybe, but definitely), I NEVER make that choice. However, I know a woman who carried a gene for hemophilia (the inability to clot blood). She did not have symptoms, but she knew that if she ever had children (specifically boys) that they WOULD have hemophilia. It was not maybe, it was absolutely guaranteed. Did she decide to not have children? Did she get her tubes tied? No. She got pregnant and had a boy. He has hemophilia and has suffered horribly. Then, she got pregnant again and had another boy. As expected, he has hemophilia too. They have both suffered an extreme amount. They both have multiple severe disabilities as a result and the medical bills alone require that both she and her husband work multiple jobs just to pay the medical bills. I understand that people have a desire to be parents, but if it s a choice between making a child suffer through life with hemophilia or adopt, adoption is the ONLY choice in my mind.