If you are going through a difficult time undoubtedly someone will encourage you by saying "have faith, it will all work out." One meaning is that you should be positive because being negative makes it worse. There are no guarantees. But having faith demonstrates that you are optimistic and are hoping for a good outcome. A factual prognosis may be realistic but Biblical faith has it's own rules. God "gives life to the dead and calls into being that which does not exist" (Ro 4:17). Therefore if we follow the Bible "we walk by faith, not by sight" (2Co 5:7). We become "those who are of the faith of Abraham, who is the father of us all" (Ro 4:16).
God instituted faith. He "said to Abram, 'Go forth from your country . . . to the land which I will show you; and I will make you a great nation'" (Ge 12:1-2). "Abram acted in faith and "went forth as the Lord had spoken to him" (:4). God later reminded him saying "'I am the Lord who brought you out of Ur of the Chaldeans'" (15:7). God had promised Abraham an heir saying, "'So shall your descendants be'" (:5). "'Abraham believed God'" (Ro 4:3) and "'faith was credited to Abraham'" (:9).