William Shakespeare: Like as, to make our appetite more keen

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 meetness
To be diseas'd, ere that there was true needing.
Thus policy in love, to anticipate
The ills that were not, grew to faults assur'd,
And brought to medicine a healthful state
Which, 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.