If a man is drowning in the water then he should have faith / hope that somebody will come and save him.
If this man has a strong hope that somebody will save him, he still allows for the possibility that nobody will do. He is very hopeful, but he's still only hoping. If he suddenly feels some doubts about his hope, he may dwell on these doubts, because hope does not forbid it.
If this man has a strong faith that somebody will save him, he refuses to admit even the possibility that nobody will do. He may feel some doubts deep inside but he will suppress such doubts with all his willpower, because he has faith. Entertaining doubts would be a betrayal of his faith.
Hope is often based on mundane inferences: "I read in newspapers about drowning people being saved. I know that there are boats often crossing this part of the river (lake, ocean)."
Faith is often based on the supernatural: "I have a guardian angel, he will make some fishermen notice me and hurry to the rescue."
P.S. This is really a philosophical question. You might try asking it at (on?) Philosophy Stack Exchange.