half the battle

A figure of speech that goes back centuries. Although the collocation knowing is half the battle long predates the G.I. Joe cartoon series, its pop-culture ubiquity in the 21st century is explained by that popularization.

half the battle

1. A large part of what it takes to accomplish something.

   Knowing is half the battle. ― It is necessary to be informed in order to do the right thing in a given situation.

• “half the battle” (US) / “half the battle” (UK) in Macmillan English Dictionary.
• “half the battle”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present.
• “be half the battle” in Longman Dictionary of Contemporary English, Longman.