Belief in something is an act of internal trust, not a demonstration of that thing’s objective existence.

Faith at the Intersection of Belief and Reality

Belief in something is an act of internal trust, not a demonstration of that thing’s objective existence. That is, even if we are firmly convinced of the existence of the external world or some object, our conviction is not directly based on experience or strict logic. As noted in one source:
"If nothing existed except concepts and representations, our definition of that which exists as conceivable and as manifest, as an objective representation and an objective concept or idea, would be complete...

So how do we know of such existence?

... The acknowledgment of the reality of external phenomena... — this acknowledgment does not have sufficient logical foundation in our perception... but only through faith — the third factor of our cognition." (source: link txt)

In other words, our confidence in external reality is not the result of an indisputable fact, but rather an assumption necessary for organizing our understanding. The same assertion is made in another statement:
"Thus, even the most external form of cognition in its objective sense is based on faith. ... Unconditional existence cannot be given by either experience or logic, but only by faith: we believe that an object is something in itself." (source: link txt)

These reflections demonstrate that faith, however deep and sincere it may be, cannot serve as a guarantee of the objective existence of anything, as it does not provide us with reliable empirical or logically grounded evidence of the presence of that object in a reality independent of ourselves.

Supporting citation(s):
"If nothing existed except concepts and representations, our definition of existence... — the acknowledgment of such reality does not have sufficient logical foundation in our perception... but only through faith — the third factor of our cognition." (source: link txt)
"Thus, even the most external form of cognition... is based on faith. ... Unconditional existence cannot be provided by either experience or logic, but only by faith: we believe that an object is something in itself." (source: link txt)