Forewarned is forearmed

1. Those who know that something is coming are better prepared to face it than those who do not know.

Idioms and Phrases

Knowledge in advance enables one to be prepared, as in Let me know when he's in town so I can take the phone off the hook—forewarned is forearmed. This expression originated as a Latin proverb, Praemonitus, praemunitus, which was translated into English by the early 1500s. It soon was put to broader use than its original military applications.