Three opposites negate the power of fretting: Trust, delight, and commit.
We only have so much mental, physical, and emotional energy. If we spend it, it is spent. If we spend it fretting about something that takes care of itself, then we have wasted it.
Evil doers, their successes, their deeds, and their devices have an expiration date. We all do. They, as we, set their courses by choices.
We do not have to supervise their outcomes to insure that evil is not rewarded or that it is left unchecked. It is not our job to meddle and it wastes our energy.
While we are called to work for justice for others and to hold out the way of righteousness, repentance, and grace, it is not our assignment to exercise judgment - even within our own minds and hearts.
If a man we once knew to be evil turns, it is because something wonderful has happened in his heart. If not, it is deeply sad, but our ultimately sadness is for him and for the God who grieves for His loss of one He has loved and invited to return - a faded blade of grass and a withered herb.
"Fret not yourself because of evildoers;
be not envious of wrongdoers!
For they will soon fade like the grass
and wither like the green herb."
(Psalm 37:1-2 ESV)