A man ought to avow his opinions and defend them with boldness.

For where is the man that has incontestable evidence of the truth of all that he holds, or of the falsehood of all he condemns; or can say that he has examined to the bottom all his own, or other men's opinions? The necessity of believing without knowledge, nay often upon very slight grounds, in this fleeting state of action and blindness we are in, should make us more busy and careful to inform ourselves than constrain others.

Although every man necessarily believes that every particular opinion which he holds is true (for to believe any opinion is not true, is the same thing as not to hold it); yet can no man be assured that all his own opinions, taken together, are true. Nay, every thinking man is assured they are not, to be ignorant of many things, and to mistake in some, is the necessary condition of humanity.

Man is what he believes.

Man prefers to believe what he prefers to be true.

Women may be vain, but when a man is vain, it is beyond believing, for a man is willing to die for his vanity.

Vanity is so firmly anchored in man's heart that a soldier, a camp follower, a cook or a porter will boast and expect admirers, and even philosophers want them; those who write against them want to enjoy the prestige of having written well, those who read them want the prestige of having read them, and perhaps I who write this want the same thing.

If human nature were not base, but thoroughly honourable, we should in every debate have no other aim than the discovery of truth; we should not in the least care whether the truth proved to be in favour of the opinion which we had begun by expressing, or of the opinion of our adversary. That we should regard as a matter of no moment, or, at any rate, of very secondary consequence; but, as things are, it is the main concern. Our innate vanity, which is particularly sensitive in reference to our intellectual powers, will not suffer us to allow that our first position was wrong and our adversary’s right. The way out of this difficulty would be simply to take the trouble always to form a correct judgment. For this a man would have to think before he spoke. But, with most men, innate vanity is accompanied by loquacity and innate dishonesty. They speak before they think; and even though they may afterwards perceive that they are wrong, and that what they assert is false, they want it to seem thecontrary. The interest in truth, which may be presumed to have been their only motive when they stated the proposition alleged to be true, now gives way to the interests of vanity: and so, for the sake of vanity, what is true must seem false, and what is false must seem true.

Demosthenes noted, “What a man wishes, he will believe.” And

Man is what be believes.” — Anton Chekhov

You know, the bigger the things a man believes in, the more fiercely he despises those who don't. And yet the greatest of all beliefs would be to believe in people.

Yet do I believe that all this is true, which indeed my reason would persuade me to be false; and this I think is no vulgar part of faith to believe a thing not only above, but contrary to reason, and against the argument of our proper senses.

The main requirements seem to be: audacity and a joy in defiance; an iron will; a fanatical conviction that he is in possession of the one and only truth; faith in his destiny and luck; a capacity for passionate hatred; contempt for the present; a cunning estimate of human nature;

According to his opinion, man should only believe what he can grasp with his intellectual faculties, or perceive by his senses, or what he can accept on trustworthy authority. Beyond this nothing should be believed.