Too much of a good thing

Meaning

Excess may do you harm.

Origin

The Oxford Dictionary of Quotations lists this phrase as proverbial and dates it from the late 15th century. Th earliest example that I can find of it in print is from Shakespeare's As You Like It, 1600:

ROSALIND: Why then, can one desire too much of a good thing?
Come, sister, you shall be the priest and marry us.
Give me your hand, Orlando. What do you say, sister?

See other phrases and sayings from Shakespeare.