Jaedon, the verse in Hebrews you quoted simply speaks to a Christian believing without yet seeing the promises afforded by God, and not that he has not been given good reason to support his belief in these promises. Notice the words assured expectation. Thus the writer is saying the Christian has assurance for what he expects his faith to bring him in the end as opposed to his faith being just a gamble that the Bible may be right about what it promises him for the future.