DM for about a year now. I'm sometimes excessively lenient to my players, because as many obstacles I love throwing their way, to me it's about the fun and hanging out, just as much as it is the joy of seeing them overcome said obstacles.

Today, they faced some Rutterkins which have a DC wisdom saving throw, and if they are unaffected or break free of the frightened effect, they remain immune to similar frightening from the same type creature for 24 hrs. One PC abided by the rule to not move aggressively toward the fiend, but stated he would not use an action because he knew he would have a disadvantage on attacks made against said creature. He succeeded on the wisdom save, and decided on his second turn he would remain back and hold an action in case the creature approached. I informed at this time that he was no longer frightened, and therefore could proceed towards the enemy if he chose to retcon his choice. Am I being too forgiving or lenient, or is this a fair discussion of the rules that one might not be aware of during their turn?