Quote 28
PROSPERO
I pray thee, mark me.
I, thus neglecting worldly ends, all dedicated
To closeness and the bettering of my mind
With that which, but by being so retired,
O'erprized all popular rate, in my false brother
Awaked an evil nature, and my trust,
Like a good parent, did beget of him
A falsehood in its contrary as great
As my trust was, which had indeed no limit,
A confidence sans bound. (1.2.108-117)
Prospero suggests that Antonio's taste of power awakened in him an even bigger desire for power. Prospero's loyalty to his brother was so great, and his trust so complete, that he really didn't see this coming. That, of course, allowed Antonio to take it farther.
Quote 29
PROSPERO
The rarer action is
In virtue than in vengeance. They being penitent,
The sole drift of my purpose doth extend
Not a frown further. (5.1.35-38)
Prospero is honest here, as he forgives everyone that's wronged him as soon as they're in front of him. It is pretty clear, though, that neither Antonio nor Sebastian is penitent about their awful behavior. Does it make sense that Prospero entirely ignores this?
Quote 30
PROSPERO
If thou more murmur'st, I will rend an oak
And peg thee in his knotty entrails till
Thou hast howled away twelve winters. (1.2.349-351)
Prospero may not be forgiving or compassionate by nature, as he's accustomed to being unquestioned and a little tyrannical. It's interesting that Ariel is actually the one who inspires Prospero to be merciful to his enemies in the end.