Faith and doubt are really inseparable; we are born with the unlimited Buddha Mind, and we naturally embrace both sides. But we don't usually live that way. Instead, we pick and choose, favoring one thing over another; and as we go through life we tend to be more and more narrow. If we try to separate faith from doubt, we create problems for our practice. We may want to embrace only faith, but then we live in fear of losing it and falling into doubt. When faith can be lost to doubt, what good is it? Some of the great mystics have described what it is like to lose all faith, and it's a discovery each one of us can make. To lose what we think of as faith is really to lose belief — belief in something. And when that happens, instead of falling into confusion and despair, we discover true faith — faith that doesn't depend on anything.
When we embrace both faith and doubt, we open ourselves up to the unknown. By living this experience from moment to moment, we manifest the unknown, our unfixed Buddha nature. Sometimes fear will come up, but instead of suppressing or running away from it, we can learn to surrender and just be with it. Living with our fear of the unknown means admitting our vulnerability: we can't understand this life, and we really can't count on anything. Nothing abides. Anything we grasp is just an idea, a temporary illusion of security, and to attach hopes to it will only lead to more suffering.
— Dennis Genpo Merzel, The Path of The Human Being