Madness

"Dream not, Coleridge, of having tasted all the grandeur and wildness of fancy till you have gone mad!" Charles Lamb

"You're only given a little spark of madness. You mustn't lose it." Robin Williams

“Madness in great ones must not unwatched go.”
Hamlet. Putin is not mad (he might be a psychopath but they are abnormally sane). Nor, so far, is Trump.

"Great wits are sure to madness near allied, 

And thin partitions do their bounds divide." 

John Dryden

"The old maxim, indeed, that "Great wits to madness sure are near allied," the maxim of Dryden and the popular maxim, I have heard disputed by Mr. Coleridge and Mr. Wordsworth, who maintain that mad people are the dullest and most wearisome of all people. As a body, I believe they are so." 

Thomas De Quincy

“I had noticed that both in the very poor and very rich extremes of society the mad were often allowed to mingle freely.”
Charles Bukowski

“All the world is queer save thee and me, and even thou art a little queer.” 

Robert Owen writing to his best friend - as a Quaker he used the second person singular, thou and thee.

"A question that sometimes drives me hazy: am I or are the others crazy?" 

Albert Einstein

“The madman is not the man who has lost his reason. The madman is the man who has lost everything except his reason.” G.K. Chesterton

“Madness is something rare in individuals — but in groups, parties, peoples, and ages, it is the rule.” 

Friedrich Nietzsche, a familiar quotation but always topical and therefore worth repeating

“Be silent and listen: have you recognized your madness and do you admit it? Have you noticed that all your foundations are completely mired in madness? Do you not want to recognize your madness and welcome it in a friendly manner? You wanted to accept everything. So accept madness too. Let the light of your madness shine, and it will suddenly dawn on you. Madness is not to be despised and not to be feared, but instead you should give it life...If you want to find paths, you should also not spurn madness, since it makes up such a great part of your nature...Be glad that you can recognize it, for you will thus avoid becoming its victim. Madness is a special form of the spirit and clings to all teachings and philosophies, but even more to daily life, since life itself is full of craziness and at bottom utterly illogical. Man strives toward reason only so that he can make rules for himself. Life itself has no rules. That is its mystery and its unknown law. What you call knowledge is an attempt to impose something comprehensible on life.”
Carl Jung