"Who, contrary to hope, in hope believed, so that he became the father of many nations, according to what was spoken, so shall your descendants be.” Romans 4.18
When physical conditions say no, when the circumstances say no, when the voices around you and everything else say no, it is not possible... the voice of the Almighty comes, which is even contrary to the remains of hope. That was the voice that made Abraham believed against hope. This is the faith that justifies and saves.