English proverbs, idioms and expressions related to this theme.
A fool may throw a stone into a well which a hundred wise men can not get out.
meaning that
Great barkers are no biters.
used to say that
Harm hatch, harm catch.
declares that
It is an ill bird that fouls its own nest.
means that
He who digs a pit for others falls into it himself.
If there is no enemy within, the enemy outside can do us no harm
suggests that