Fig.: to take an irrevocable decision; to commit oneself irrevocably to a particular course of action

Our decision is made, we crossed the Rubicon and there is no coming back

Ormai la decisione è presa, abbiamo passato il Rubicone e non possiamo più tornare indietro

After years of thinking Mary Lou crossed the Rubicon: she sold everything she had and left for Africa as a missionary

Dopo anni di indecisioni Maria Luisa ha passato il Rubicone: ha venduto tutto quello che aveva ed è andata missionaria in Africa

The Rubicon is a small river in northern Italy. It's only 15 miles (24 Km) long, but in ancient Roman times it was part of the boundary between Cisalpine Gaul and Italy proper, and it was forbidden by Roman laws to cross it in arms without the Senate's permission. In 49 B.C. Julius Caesar led his army across the Rubicon into Italy to march on Rome; such an action was in effect a declaration of civil war with no way back