One bad apple spoils the bunch.
More German Proverbs:
When the tale of bricks is doubled, then comes Moses.German
Pay-day comes every day.
German
Sometimes the whole nation has to pay for the foolish deed of one man.
German
Who takes the child by the hand, takes the mother by the heart.
German
Not too little, not too much.
German
The greatest wealth is contentment with a little.
German