One can never have too much of a good thing.

Meaning: Abundance of beneficial things—love, knowledge, health—enriches life without diminishment or excess.

Origin: The idea of "too much of a good thing" is proverbial from the late 15th century, and the first example in print is Shakespeare's As You Like It (1600), where Rosalind asks, "Why then, can one desire too much of a good thing?" The proverb has always had its contrary — too much of a good thing is exactly what spoils it.