The Illustrated Guide to Criminal Law Chapter 11: Excuse Me! Excuse pg 3: When is a crime not a crime?
In other words, a mistake of law will not excuse you from criminal liability.
There are other kinds of situations, however, where you might be excused. Situations where you did something that ordinarily would have been punishable as a crime… but in this case you’re off the hook.
In some cases, what you did was bad, but you’re EXCUSED for one reason or another.
The State comforting Average Joe, who’s on bended knee.
The State forgives you.
In other cases, what you did wasn’t bad at all: You were JUSTIFIED in doing it.