"Crossing the Rubicon" is a popular expression that means to go past a point of no return by doing an action so powerful that it is irreversible. It is believed that the phrase originated when Julius Caesar took his armies past the Rubicon Barrier that no general had ever crossed, and marched on to Rome. This was considered an act of war that solidified his power and changed the world forever.
Think of a fateful decision that someone has made that has had a significant and irreversible impact on the world. What was this decision and what was its short-term and long-term impact?