A common view of faith suggests that when a person has faith, there can be no uncertainty. Under this paradigm, those who speak of their beliefs feel obligated to state their beliefs as an absolute surety with no room for error or doubt. But if faith were a perfect knowledge, there would be no need for beliefs, nor would there be any need for Heavenly Father to test our faith.
In reality, faith is defined by uncertainty. Most of the time, we believe in a principle before we fully understand it. We believe in God before we know Him on a deep level. It is okay to admit that we don't know why we believe something--that is what faith is! By accepting truths and living by them without fully understanding the whys and hows, we are walking by faith.