How we cite our quotes: (Act.Scene.Line). Line numbers correspond to the Riverside edition.
Quote #1
FLAVIUS
These growing feathers plucked from Caesar's wing
Will make him fly an ordinary pitch,
Who else would soar above the view of men
And keep us all in servile fearfulness. (1.1.77-80)
Even as early as the first scene of the play, we get a sense that some Romans foresee that no good can come out of Caesar's increasing power. They predict Caesar will keep them "servile," but they can't predict the terrible outcome of their decision to assassinate him: civil war and the beginning of the end of the Roman Republic.
Quote #2
SOOTHSAYER
Beware the ides of March.
CAESAR
He is a dreamer. Let us leave him. Pass. (1.2.28-29)
Even though Caesar is warned by the soothsayer to watch his back on March 15 ("ides" means "middle"), Caesar doesn't take the ominous warning seriously. As we know, Caesar was stabbed 33 times on March 15, so it's pretty clear to the audience that Caesar should heed this warning. And even though Caesar says a few moments later that he's wary of "lean and hungry" looking men like Cassius (1.2), it seems like his arrogance prevents him from taking the soothsayer's advice to heart. This, by the way, isn't the only time Caesar ignores warning signs – later, he blows off his own wife, who envisions his death in a prophetic dream. (See 2.2 below.)
Brain Snack: In a Season 6 episode of The Simpsons called "Homer the Great," Lisa warns Homer to "beware the Ides of March."
Quote #3
Men at some time are masters of their fates.
The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings. (1.2.146-148)
As Cassius complains about Caesar's power, he claims that it's Rome's own fault for being servile to one man. Men, according to Cassius, are "masters of their fates," which means it's up to them to take down Caesar. This seems like a fine idea, but there's a lot of evidence in the play (like prophesies and omens that come true) that men don't have much control over their destinies.