From Longman Dictionary of Contemporary Englishcross the Rubiconcross the RubiconEFFECT/INFLUENCEto do something that will have extremely important effects in the future and that you cannot change → Rubicon
Examples from the Corpus
cross the Rubicon• But tormented though I was with guilt and self-doubt, I knew I had crossed the Rubicon.• On the way to political union we are now crossing the Rubicon.• General Bourbollon's troops are gathering around the capital; he's prepared to cross the Rubicon. 