PROSPERO
A devil, a born devil, on whose nature
Nurture can never stick; on whom my pains,
Humanely taken, all, all lost, quite lost;
And as with age his body uglier grows,
So his mind cankers. (4.1.211-215)
Is Caliban a victim of his nature, or is Prospero foolish for thinking it could ever be otherwise? Can both of these things be true at the same time? (It's a mental Venn diagram!)
PROSPERO
Both, both, my girl.
By foul play, as thou sayst, were we heaved thence,
But blessedly holp hither. (1.2.77-79)
Prospero has the distance and perspective of wisdom when thinking about how they ended up on the island. Antonio's treachery put them there, but the help of the natural elements, and Gonzalo's loyalty, allowed them to survive and prosper.
Quote 27
PROSPERO
Being once perfected how to grant suits,
How to deny them, who t' advance and who
To trash for over-topping, new created
The creatures that were mine, I say, or changed 'em,
Or else new formed 'em, having both the key
Of officer and office, set all hearts i' th' state
To what tune pleased his ear, that now he was
The ivy which had hid my princely trunk
And sucked my verdure out on 't. (1.2.98-106)
Prospero values the brotherly bond more than Antonio; Prospero assumed his brother would be loyal to him. Instead, Antonio learned all the tricks of political treachery while serving in the place of Prospero, and used them to betray his brother.