Carl Jung: Fanaticism is ever the brother of doubt,

Has it ever—except in the most benighted periods of history—been observed that a scientific truth needed to be elevated to the rank of a dogma? Truth can stand on its own feet, only shaky opinions require the support of dogmatization. Fanaticism is ever the brother of doubt, ~Carl Jung, CW 10, Para 335

Doubt and insecurity are indispensable components of a complete life. ~Carl Jung, Letters Vol. II, Pages 163-174

Doubt is the crown of life because truth and error come together. Doubt is living, truth is sometimes death and stagnation. ~Carl Jung, Dream Analysis, Page 89.

When you are in doubt you have the greatest opportunity to unite the dark and light sides of life. ~Carl Jung, Dream Analysis, Page 89.

He who cannot bear doubt does not bear himself. Such a one is doubtful; he does not grow and hence he does not live. Doubt is the sign of the strongest and the weakest. The strong have doubt, but doubt has the weak. ~Carl Jung, The Red Book, Page 301.

I do not doubt: I also want evil for the sake of my God. I enter the unequal battle, since it is always unequal and without doubt a lost cause. How terrible and despairing would this battle be otherwise? But precisely this is how it should and will be. ~Carl Jung, Liber Novus, Page 289.

But fanaticism is always a compensation for hidden doubt. Religious persecutions occur only where heresy is a menace. ~Carl Jung, Analytical Psychology and Education, Page 81.

Fanaticism is due to an unconscious doubt threatening the conscious attitude. For example, dogmatism is merely to protect a creed against an unrecognized doubt. True conviction needs nothing of the sort. Fanaticism is due to a threatened conviction. ~Carl Jung, Cornwall Seminar, Page 18.

Doubt is creative if it is answered by deeds, and so is neurosis if it exonerates itself as having been a phase—a crisis which is pathological only when chronic. Carl Jung, Letters Vol. 1, Pages 332-334

Neurosis is a justified doubt in oneself and continually poses the ultimate question of trust in man and in God. Carl Jung, Letters Vol. 1, Pages 332-334

I for my part prefer the precious gift of doubt, for the reason that it does not violate the virginity of things beyond our ken. ~Carl Jung, Psychology and Alchemy, Page 8.

I am just as much in doubt about myself as before, the more so the more I try to say something definite. It is as though familiarity with oneself alienated one from oneself still further. ~Carl Jung, Letters Vol. II, Pages 162-163.