The Believing Paradox
One of the most beautiful exclamations in Scripture is found in Mark 9, verse 24:
Immediately the father of the child cried out and said, “I believe; help my unbelief!”
The beauty is in the paradox. Even though we truly believe in Christ, our human nature keeps us from fully believing. At some point in life, everybody finds themselves crying out and confessing their belief and unbelief. It is at this point that we reach the end of our humanity and the beginning of Christ.

The topic of faith, or more to the point, not enough faith, has been on my mind recently too:
http://thainamu.blogspot.com/2008/02/nature-of-faith.html
http://thainamu.blogspot.com/2008/02/some-more-about-faith.html