The story
People were warning one another about too much of a good thing long before Shakespeare. The Oxford Dictionary of Quotations calls it proverbial from the late 1400s.
Shakespeare gave the old saying a playful twist in As You Like It, written around 1600. Rosalind, in love with Orlando, has fled to the Forest of Arden dressed as a young man named Ganymede. Orlando doesn’t recognize her, so she offers to “play” Rosalind and let him practice courting.
She asks Orlando, “Are you not good?” He answers, “I hope so.” Rosalind shoots back, “Why then, can one desire too much of a good thing?” For someone in love, the answer is clearly no.
Moments later she has her cousin Celia act as the priest in a pretend wedding. The audience knows what Orlando doesn’t: the wedding is pretend, but the love is real.
That is the earliest printed example on record. The everyday saying we use now is just the tail end of Rosalind’s question, minus her twinkle.
