This means that all beliefs have as part of them an implied doubt. Facts cannot be doubted, they are observably real. When belief is assumed to be fact, when this mistake is made by a mind clouded by a motivation to assume belief as fact, that belief is considered beyond doubt, just as is a fact. Beliefs beyond doubt are inherently dangerous. They are dangerous because they are often acted upon as though they were facts, and the inherent weakness of this is that a belief is not a fact.
Beliefs can be, and often are, wrong.
Children in our culture often believe in Santa Claus, in the Easter Bunny and the Tooth Fairy. To them, with their simple minds, these beliefs are facts. This is because very young children may not have developed sufficiently to discriminate between belief and fact. But even adults can fall prey to such immature thinking, because they are afraid, because they are disturbed, because they are mentally ill, because they are filled with excitement, or a whole host of reasons. Hallucinations can occur that seem so real that they convince the brain that it has experienced observable fact.