Fans of “Star Trek” are familiar with the Kobayashi Maru, but others might not be so I’ll briefly explain what it is. In the Star Trek storyline there is a simulation for aspiring ship commanders that is called the Kobayashi Maru. In it the candidate for promotion is faced with a no-win scenario. The reason is to see how the officer would react to absolute and total defeat. When done correctly and with no cheating (a plot point in the Star Trek stories) the officer will have to deal with the loss of their crew and their ship. Again, the enemy cannot be beaten. It is a test of the officer’s mettle to see if they are up to the challenges ahead.
So this brings us back to Dungeons & Dragons. While the game is devised to let Game Masters toss puzzles and challenges at the players, it is generally assumed that these are all possible to solve. This however is not necessarily how it is going to work. There is no guarantee that just because the players have an awesome array of weaponry and skills that they are going to be able to beat every villain or monster that they encounter. Sometimes the fiend is too powerful for the time being and the players need to prepare themselves more. But there are occasions (and it should be noted that these must be rare in the extreme) when the challenge is simply too great. It isn’t just the current circumstances that make the bad guy unbeatable. There is simply no way the players will ever be able to beat them. This isn’t to stifle the players, though. That would be downright sadistic.
No, the point of having an undefeatable opponent is to give the players in the game a solid and immovable force against which they can operate. With a bare minimum of such entities the rest of the game becomes much more tangible as everything else is proven malleable to a greater degree. Nations rise and fall, heroes live and die, monsters show up and are vanquished. But there must be something, or someone, that defies this temporary existence.
Not every game needs to have such an entity, of course. Only the biggest campaigns would ever need such a contrivance. As player characters develop and grow they face more difficult obstacles. At some point they will need to interact with something they cannot overcome. No matter how powerful their magic, no matter how high their skill levels, there must be something against which the players simply will never be able to claim victory over.
Unless, like Captain Kirk, they cheat.