The secret flaw is human pride. Some very religious people are counting on striving sufficiently to be worthy in the end. That is not God’s Way so they will be horribly surprised at the results of their efforts.
Yes, they are in for the utter, total, complete shock of their existence. Many, probably wondering how they can endure for all eternity. It's sad, because no one needs to be there. It really is so simple, a caveman can do it. 😀