S we see ground that lies fallow, teeming, if rich and fertile, with countless kinds of wild and useless plants, and observe that, to keep it serviceable, we must master it and sow it with various crops of use to ourselves; and as we see that women, of themselves, sometimes bring forth inanimate and shapeless lumps of flesh, but to produce a sound and natural birth must be fertilized with different seed, so it is with our minds. If we do not occupy them with some definite subject which curbs and restrains them, they rush wildly to and fro in the ill-defined field of the imagination,

As water, trembling in a brass bowl, reflects the sun's light or the form
of the shining moon, and so the bright beams flit in all directions,
darting up at times to strike the lofty fretted ceilings.–Virgil, Aeneid, VIII, 22

And there is no folly or fantasy that they will not produce in this restless state.

Unreal monsters am imagined, like a sick man's dreams.– Horace, Ars Poetica, 7.

The mind that has no fixed aim loses itself, for, as they say, to be everywhere is to be nowhere.

A man who lives everywhere, Maximus, lives nowhere.–Martial, VIII, 73.

When lately I retired to my house resolved that, in so far as I could, I would cease to concern myself with anything except the passing in rest and retirement of the little time I still have to live, I could do my mind no better service than to leave it in complete idleness to commune with itself, to come to rest, and to grow settled; which I hoped it would thenceforth be able to do more easily, since it had become graver and more mature with time. But I find,

Leisure always breeds an inconstant mind.–Lucan. IV, 704.

that, on the contrary, like a runaway horse, it is a hundred times more active on its own behalf than ever it was for others. It presents me with so many chimeras and imaginary monsters, one after another, without order or plan, that, in order to contemplate their oddness and absurdity at leisure, I have begun to record them in writing, hoping in time to make my mind ashamed of them.