Rubicon

To commit to a particular plan or course of action. The phrase refers to how Julius Caesar crossed the Rubicon river and became embroiled in civil war in 49 BCE. Look, if you cheat on this test, you are passing the Rubicon, man. You can't take that back. I think I passed the Rubicon when I took this management position. It would be a huge pay cut to go back to my old job, and my boss would be furious.

Fig. to do something that inevitably commits one to following a certain course of action. (Alludes to the crossing of the River Rubicon by Julius Caesar with his army, which involved him in a civil war in B.C. 49.) Jane crossed the Rubicon by signing the contract. Find another job before you cross the Rubicon and resign from this one.

to make a decision that cannot be changed later When I quit editing and decided to be a writer, I had crossed the Rubicon to an uncertain future.

to do something which will have very important results, which cannot be changed later International pressure may be able to prevent the country crossing the Rubicon to authoritarian rule.

Irrevocably commit to a course of action, make a fateful and final decision. For example, Once he submitted his resignation, he had crossed the Rubicon. This phrase alludes to Julius Caesar's crossing the Rubicon River (between Italy and Gaul) in 49 b.c., thereby starting a war against Pompey and the Roman Senate. Recounted in Plutarch's Lives: Julius Caesar (c. a.d. 110), the crossing gave rise to the figurative English usage by the early 1600s.