Either don't try at all or make damned sure you succeed.
Aut non rem temptes aut perfice.
Original text (Latin)
Notes from Wikiquote
Book I, line 389 (tr. James Michie)
Original text (Latin)
Quote text and notes from Wikiquote: Ovid (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.