There is a notion adrift everywhere that imagination, especially mystical imagination, is dangerous to man's mental balance. Poets are commonly spoken of as psychologically unreliable; and generally there is a vague association between wreathing laurels in your hair and sticking straws in it.

Facts and history utterly contradict this view. Most of the very great poets have been not only sane, but extremely business-like; and if Shakespeare every really held horses, it was because he was much the safest man to hold them. Imagination does not breed insanity.

Exactly what does breed insanity is reason. Poets don't go mad; but chess players do. Mathematicians go mad, and cashiers; but creative artists very seldom. I am not, as will be seen, in any sense attacking logic: I only say that this danger does lie in logic, not in imagination. Artistic paternity is as wholesome as physical paternity. Moreover, it is worthy of remark that when a poet really was morbid it was commonly because he had some weak spot of rationality on his brain. Poe, for instance, really was morbid; not because he was poetical, but because he was specially analytical. Even chess was too poetical for him; he disliked chess because it was full of knights and castles, like a poem. He avowedly preferred the black discs of draughts [i.e. checkers, Fox], because they were more like the mere black dots on a diagram.

Perhaps the strongest case of all is this: that only one great English poet went mad, Cowper. And he was definitely driven mad by logic, by the ugly and alien logic of predestination. Poetry was not the disease, but the medicine; poetry kept him in health.

I interrupt the words of Chesterton to quote a bit of verse from Cowper. Twas he that penned the lovely hymn of God's providence that began, "God moves in a mysterious way, His wonders to perform; He plants His footsteps in the sea, and rides upon the storm." Back now to Chesterton: 

He [Cowper, Fox] could sometimes forget the red and thirsty hell to which his hideous necessitarianism [i.e. predestination, Fox] dragged him among the wide waters and the white flat lillies of the Ouse [the English river where Cowper attempted to take his own life, Fox]. He was damned by John Calvin [proponent of predestination, Fox]; he was almost saved by John Gilpin [Cowper's comic alter ego, featured in a ballad penned by the poet, Fox]. Everywhere we see that men do not go mad by dreaming. Critics are much madder that poets.

Homer [the Greek poet, not the doughnut munching Mr. Simpson, Fox] is complete and calm enough; it is his critics who tear him into extravagant tatters. Shakespeare is quite himself; it is only his critics who have discovered that he was somebody else [an allusion to the theory that Sir Francis Bacon wrote the works attributed to Shakespeare; remind me to tell you a funny story about that sometime, Fox] .

And although St. John the Evangelist saw many strange monsters in his vision [i.e. The New Testament's Revelation epistle, Fox], he saw no creature so wild as one of his own commentators.

Here now, in the final two paragraphs of this lengthy quotation, is Chesterton's insightful conclusion:   

The general fact is simple. Poetry is sane because it floats easily in an infinite sea; reason seeks to cross the infinite sea, and so make it finite. The result is mental exhaustion...To accept everything is an exercise, to understand everything a strain. The poet only desires exaltation and expansion, a world to stretch himself in.

The poet only asks to get his head into the heavens. It is the logician who seeks to get the heavens into his head. And it is his head that splits" (G.K. Chesterton, Orthodoxy, pp. 9-10). 

How might you articulate the difference between poetry that "floats easily in an infinite sea" and reason that "seeks to cross the infinite sea, and so make it finite"? What's the pragmatic, heart and soul, learning?