Truth is the one of the two face values of the connection between an assertion and the reality. "Knowing" that X (statement) is true is the realization (maybe right or wrong, information to which the agent has no access to) of the existence of the connection in a way of gathering enough information to do that. "Truth" here is value (of the connection) such that the assertion completely describes the objective reality to our relevance.
"Believing" is making another artificial connection between the assertion (not the reality) and the intelligent mind while being unsure of the first connection that X holds with reality. It is as if the reality is behind the assertion, we are facing assertion and hence can't "see" the objective reality.
Now while stating these it is assumed that the ultimate reality is inaccessible by the agent (only the "Supreme" accesses that). The "reality" here is the form in which it is consumable and relevant to the agent.
It is this form of "believe" that makes the agent conceive the failure of its "believe" because he is aware of the bridge that believe is and that this bridge may take it the wrong way. And that the agent is in search of the reality and won't even be on the bridge (believe) that it is if it was aware it was not the one it was looking for (the believe is wrong).