As an example of this lets take "The great escape" re. getting Phillipa out of of her cell.
This quest is a main quest and was 4 levels lower than my current level.
Most of the guards were very easy to kill. Then on reaching the guy in his room
with the cellar key he had that red skull above his head. The game suggests coming
back when on a higher level. Any higher then I would receive no XP points.
Anyway, it was too late to retreat.
I eventually killed him but only by throwing dancing bombs at him, but this does not bode
well for what lies ahead as the game reaches its climax.