Consider whether statements (1) and (2) are true:
(1) If X is true, then I believe X.
If one does not accept this, then one accepts the opposite: one would be willing to state "X is true and I do not believe X." But that is clearly a contradiction for any particular X. Therefore, we must accept that (1) is true for all X.
(2) If I believe X, then X is true.
The negation of this would be saying "I believe X and X is false." Again, this is impossible to state consistently for any X. So statement (2) is also true for all X.
But (1) means I am omniscient, and (2) means I am omnipotent. Cool, I never knew that!