I'll be honest, people who claim and act as if they have no doubts frighten me. They frighten me whether they believe in God or not. I sometimes wonder, "Don't aggressive atheists ever doubt their unbelief?" On the whole, believers seem pretty straightforward in admitting that we sometimes doubt.
In his posthumously collected and published work On Certainty, Wittgenstein made an important distinction "between the concept of 'knowing' and the concept of 'being certain.'" He goes on to note that this distinction isn't really a significant one at all, "except where 'I know' is meant to mean: I can't be wrong" (3e). Hence, when Von Balthasar, Giussani, Ratzinger, et al. insist that faith and reason work together to help us arrive at knowledge, they are not making a mistake by including faith in their epistemological assertions.
In his book The Religious Sense Giussani gives a rather detailed example of how it is we employ what can really only be called "faith" to grasp even everyday things that we would not hesitate to say we "know," even while admitting there is a possibility we're wrong. Giussani rightly points out "that man can err using the scientific, philosophical, or mathematical methods" (22). His point is that making a mistake when employing one of these methods does not necessarily invalidate the method being employed. One the things about which Giussani was fervent is that faith, too, must have a method. Such a method is not something esoteric, or even really unique to believers.
The late Michael Spencer, better known, perhaps, as the "InternetMonk," or, simply "IMonk," once confessed: "I wonder if God exists. I sometimes see the universe as an empty place. Oh, I frequently see it filled with the glory of God and singing his majesty with all its created energy. I’m often filled with the assurance of faith. But not all the time. Sometimes tragedy, emotion, age, disappointment, depression, dark moods….they visit me and I doubt. I wonder and question. This is my human experience. God gives me faith. My humanness still gives me doubt."
Some knowledge claims can only be sensibly arrived at by the use of what is called defeasible reasoning. Defeasible reasoning is a certain type of non-demonstrative reasoning. By non-demonstrative is meant that one does not arrive at a complete or definitive demonstration of the knowledge claimed by employing defeasible reasoning. When it comes to God, when it comes to the great question of being (Why are there things rather than no-thing?), so painstakingly retrieved by Heidegger, how could it be otherwise?
Very often it seems to me that unbelievers claim to have much more certitude than most believers would ever dare claim. Personally, I don't think that kind of certitude has much epistemic warrant. Rather, I think the mystery of being requires a lot of humility for believers and unbelievers alike.