a problem that spoils something that is otherwise good
—We are so glad that my brother will be here for the holiday. The only fly in the ointment is that he can’t stay longer.
Ecclesiastes includes several of Solomon’s proverbs. One of them uses a vivid picture to show that good judgment can be ruined by a little bit of foolishness:
One dead fly makes the perfumer’s ointment give off a rancid stench [Dead flies cause the ointment of the apothecary to send forth a stinking savour—],
so a little folly can outweigh much wisdom. (Ecclesiastes 10:1)