Fudging or Constructive Cheating (TCG)

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Imagine that during the course of the game, the player characters have just barely survived the climactic encounter with the Baron Skorditch, Wizardlord of the Kroolons, escaped with the cumbersome princess Natasia and discovered the lost secret of double-entry bookkeeping. All that stands between them and glory is 100 feet of corridor. Unfortunately, the DM had decided long ago (more likely at 3 AM. the night before) that this corridor would be filled with deadly Snargon gas. Since none of the players thinks to check for traps, the DM secretly makes the die rolls for them.
All-too-suddenly, the hot dice-rolling that allowed the pes to so handily overcome their earlier obstacles goes sour. No one detects the gas. If the party continues, they will all die! And, of course, they continue...
While the DM should not feel that he must protect his precious plot lines or make sure that the desired outcome of a story takes place, he does have a responsibility to his players. He owes them a good time.
Having the entire party wiped out as the denouement of an adventure is rarely considered a good time. In situations like these, it's OK for the DM to cheat
Throughout these chapters on DMing, it will be stressed time and time again that the DM must remain impartial. He should not take the side of the monsters against the PCs or side with the player characters in their battle against their fiendish foes.
So now we tell the DM to cheat! What should the fair DM do in such a situation? Well, a hard-hearted DM would let the pes walk into his trap, blow their saving rolls, and die. He may also see his players suggest, that they have better things to do with their time from now on.
At the other extreme, the DM could just say to himself "there's no trap here" and let the PCs proceed on their way, not realizing that the DM just compromised his design to let them live. This too is a mistake, because by doing so, the DM has assumed that the players are unable to deal with challenges.
A wiser solution would be to suggest to the players that something does not seem right in the corridor ahead or to let an NPC reveal the trap, even though it costs his life. The DM might even improvise an ambush attack that diverts the characters to another exit.
In a sense, whenever a situation arises in which the outcome of the entire adventure seems to hang on a single die roll, and that die roll fails, the DM is encouraged to fudge-to cheat in a constructive manner. Rather than see an entire gaming session, even an entire campaign wasted because of one stupid incident, the DM may wish to create alternative outcomes on the fly, ones that require roleplaying instead of "roll-playing."