Zen In The American Grain: Discovering The Teachings At Home, by Kyogen Carlson

More on the subject of doubt:

So what is this 'honest doubt' that Tennyson connects with faith? To hold an honest doubt is to want to know, above all, 'What is true?' It is not negative skepticism to ask 'Is my understanding of this correct?' or, 'Is this really what it represents itself to be?' An honest doubt, with a little humility, is necessary for the recognition that Truth is so immense, so vast, that our understanding of it can only be quite small. While humbling, this recognition leaves us open to endless possibilities.