Doubt cannot override a certainty

The human spirit glows from that small inner light of doubt whether we are right, while those who believe with certainty that they possess the right are dark inside and darken the world outside with cruelty, pain, and injustice.

If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.

Doubt is to certainty as neurosis is to psychosis. The neurotic is in doubt and has fears about persons and things; the psychotic has convictions and makes claims about them. In short, the neurotic has problems, the psychotic has solutions.

Doubt is not a pleasant condition, but certainty is absurd

If a man will begin with certainties, he shall end in doubts: but if he will be content to begin with doubts, he shall end in certainties.