One scabbed sheep will taint a whole flock.
More Turkish Proverbs:
The plumber's house always leaks.Turkish
To listen to a lie is harder than to tell it.
Turkish
Every sheep will be hanged from its own legs.
Turkish
An orphan cuts his own umbilical cord.
Turkish
A son will learn from his father to make a living, a daughter will learn from her mother to cut clothes.
Turkish
If the bald man knew a remedy he would rub it on his own head.
Turkish