Too much of a good thing. We naturally desire good things, and are familiar with this expression. Here for further reflection are variations on the theme:

“For whoso hath too much of any good, of that same good he shall soon be bereft.” The Fall of Princes, John Lydgate (c.1370 – c.1451)

“Too much of a good thing is never a good thing.” @whatnow2do

“Too much of a good thing is a bad thing.” Unknown

“As people do better, they start voting like Republicans – unless they have too much education and vote Democratic, which proves there can be too much of a good thing.” Karl Rove

“To much of a good thing is just about right.” Jerry Garcia (1942 – 1995)

“Too much of a good thing can be wonderful.” Mae West (1893 – 1980)

“Too much of anything is bad, but too much good whiskey is barely enough.” Mark Twain (1835 – 1910)