To tie why the Deck of Many Things back into board games, consider the following variant rule for Chess:

Once per game, instead of making a move, you can roll a die. On a 1-3, you have to remove one of your rooks from the board. On a 4-6, you get to replace a knight or bishop. (Your opponent gets to choose what square in your back row the piece appears in, so you won’t be able to use this for immediate tactical advantage. You can’t use the ability if you have no rooks to sacrifice)

Is this fair? Well, in a sense, yes, because it’s available to both players, and you stand to lose more material than you gain. But the game would be no fun, because the randomness introduced by the new rule would dominate the game. Consider equally matched players. The game would progress until one player gained an advantage that looked decisive. At that point, the losing player would exercise the special option. If the roll turned out badly, no big deal; the game was going to turn out badly anyway. If the roll succeeds, the tables are suddenly turned (adding a knight is usually more than enough to turn a decisive loss into a decisive victory) and the other player is suddenly forced to use the option. If the other player also succeeds, the effects of the special rule are meaningless. If the other player happens to fail, the game is finished.

So, the final net effect of this optional rule is to add a flat 25% chance that the losing player wins the game instead. Like the Deck, it’s sudden and immediate; if you win, you don’t feel like you deserved it. It’s a little different in that you don’t have to be desperate to draw from the Deck, although that would certainly be the best use of it when considering risk vs. reward.