Anger and resentment drains your energy, and keeps you imprisoned by your past. By choosing to let go of your hurt and anger, you give yourself the freedom to fully experience joy in life. Anger builds inside us, so by letting go, you improve your ability to control your anger. We've all seen the person who blows up at the smallest incident. It is the accumulation of built up anger that is unreleased that causes this explosion.
It's normal and natural to resent certain experiences; those that take us far outside the control we never would surrender. Enter the grief experience. It's why our first cataclysmic grief experience teaches us so much.