What would happen if a duelist didn't follow the instruction on the card?
The duel disk contains an advance A.I. that is programmed to imply the rules of the game and figure out the rulings of the cards. During the battle city tournament, Joey wanted to summon Giltia the D. Knight, however it didn't appear on the field because it was a level 5 monster and Joey didn't tribute a monsters to summon it. Meaning that unless the conditions are not met, the A.I. will prevent certain cards from being played. This is the earliest example of the duel disk preventing players from making mistakes with their cards during a game. 

I hope that my answer was helpful and fun to read. :)