Doubt

Doubt whom you will, but never yourself.
- Christian Nestell Bovee, 1820 - 1904

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.
- René Descartes, 1596 - 1650

If a man will begin in certainties he shall end in doubts; but if he will be content to begin in doubts he shall end in certainties.
- Francis Bacon, 1561 - 1626

Doubt is uncomfortable, certainty is ridiculous.
- François Marie Arouet (Voltaire), 1694 - 1778

Give me the benefit of your convictions, if you have any, but keep your doubts to yourself, for I have enough of my own.
- Johann Wolfgang von Goethe, 1749 - 1832

I suppose it is much more comfortable to be mad and not know it than to be sane and have one's doubts.
- G. B. Burgin