Caesar had the opinion that the senate was nothing but a bunch of fools only arguing over their own interests rather than the interest of Rome. Therefore he desired to end the republic and to be a king again, and being the most successful army leader he could count on the support of many, since army leaders had officially not more power than politicians, but in reality they had.
The Senate did not want that to happen. After all the Romans swore never to allow a king again. This is when they hired an other general, Pompey to stop Caesar and deny him access to Rome. At the river Rubicon, Caesar decided to attack Pompey's troops and by doing so he violated one of the highest laws of the Roman Republic, and Caesar knew the consequences would be severe.
This is when he pronounced the legendary words "ALEA IACTA EST", meaning "THE DIE HAS BEEN CAST". In other words, there is no way back now, I'll have to face the consequences of my actions, regardless of their motivation, and nobody can tell what the outcome will be...
Now for the Think Thank there is this question. I doubt yours will be as big as Ceasar's (or did you actually lead an army about to attack another army of your own nation?), but did you ever have your own ALEA IACTA EST moment. A moment in which you were doing something you knew you had to do, but of which you knew the consequences could also be pretty bad for you, but that you knew you had to risk is, as there was no way back now?