Crossing the Rubicon is a phrase that has survived many centuries. It is essentially used as a metaphor to mean - point of no return. In other words once you cross a certain line, there's no turning back.
The story behind this phrase lies in Roman history. When Julias Caesar was asked by the Roman Senate to relinquish his position as a the Governor and Commanding officer of the army of Gual province north-east of Italy, he refused. Instead on January 10th 49 BC he and his army marched towards the Republic to overthrow the government.
In doing so, they crossed the Rubicon river - which basically acted as the border between the Gaul region and the Italian region (main)
This action of Caesar led to Roman Civil War and eventually led to the Roman empire lasting almost till mid of 5th century.
This phrase has always fascinated me. We do have instances in our personal and professional life where we cross the line and realize there's no point of return. It could be relationship specific. It could be project specific. It could be investment specific. Once you "cross the Rubicon", there's no turning back.
Usually the crossing of the Rubicon is an emotional reaction to an external trigger. Your mind is so made up after that trigger, you see no point in moving back.
A good example of this could happen during an election campaign. If there are some voters sitting on the edge watching the nominees battle it out and if some candidate behaves or acts in a certain way or says something that you cannot reconcile with, that basically is the proverbial crossing of the rubicon. Now there's no point of backing that candidate. I have seen it happen many times.
You are cutting him some slack, you are giving him the benefit of the doubt, all along observing his work, his moves, his conversations. But if he says or does something that is so stupid that there's no way you can justify it to yourself, that essentially is the line that is drawn.
And if it's a close race, one stupid remark or statement can become the proverbial crossing of the Rubicon.
Humans by nature have an internal compass where they can make a judgment call and figure out a trade off between what they can sustain versus what they cannot... After allowing something to go on for too long, there can be a trigger, a catalyst kind of moment that basically tells you - this is enough and the situation is at a point of no return. That's the moment of "crossing of the Rubicon"