Yep. The game had a “Wall” effect which would bounce any spell you cast on them back on yourself. But, what if both the players and the monsters both had Wall

Yep. The game had a “Wall” effect which would bounce any spell you cast on them back on yourself. But, what if both the players and the monsters both had Wall active? That situation would have an infinite recursion problem. The solution for the game was to say that a spell could only bounce once. That solution led naturally to monsters that always had Wall up and would cast a lot of spells so that you could defeat them by using Wall on yourself.