In almost every tradition, the first instinct is to treat doubt as the enemy — as something to be overcome, suppressed, or confessed. The deeper traditions know otherwise: that doubt, properly held, is the instrument by which faith is refined. The Zen koan is structured doubt; the Talmudic argument begins with contradiction; Rumi's reed flute cries because it has been separated from the reed bed and does not know if it will return — and that not-knowing is itself the music.
Each step builds on the last.