Shakespeare's Sonnet 118

Like as, to make our appetite more keen,With eager compounds we our palate urge;As, to prevent our maladies unseen,We sicken to shun sickness when we purge;Even so, being full of your ne’er-cloying sweetness,To bitter sauces did I frame my feeding;And, sick of welfare, found a kind of meetnessTo be diseas’d, ere that there was true needing.Thus policy in love, to anticipateThe ills that were not, grew to faults assur’d,And brought to medicine a healthful stateWhich, rank of goodness, would by ill be cur’d;But thence I learn and find the lesson true,Drugs poison him that so fell sick of you.

Just as we sharpen our appetite by stimulating our taste with sour mixtures, and make ourselves sick with purges to prevent diseases we cannot yet see, so I, full of your sweetness that could never grow tiresome, turned to bitter sauces for my meals. Sick of being well, I thought it somehow fitting to become diseased before there was any real need. So my strategy in love, meant to prevent troubles that did not exist, became a source of certain wrongs. It brought medicine to a healthy condition that, supposedly too full of goodness, would be cured by something bad. But from this I learn, and find the lesson true: medicines poison the man who became sick of you that way.