Simple example: The party is attacking their nemesis, and they have enlisted the help of an NPC ally. A battle ensues, the nemesis gets low on hit points, an NPC swings and hits, and rolls enough to kill. The next few actions are all by PCs.
The DM cheats by giving the nemesis some extra hit points, so a player can be the one to defeat him. Later the DM lies about it because revealing this cheat would make players feel worse than just letting the NPC die.
I understand this philosophy and I can see why people would do it. If that's what your group likes then how could I possibly object.
But for me, I look at that situation and see it differently. The DM is worried that the players will feel like they have no involvement, that everything is in the DM's court because an NPC was slain by an NPC. This isn't the case, it's just some random chance. The dice are to blame, not the DM. But in order to avoid the
appearance of the players having no role, they're given the actual fact of their contributions being ignored by the DM who then covers the whole thing up wtih a lie.
The PCs chose to involve the NPC ally, and that decision and its relevant consequences are being ignored.
The PCs selected tactics that resulted in that outcome and now can't adjust their tactics because they haven't realized how effective they are/aren't.
On a more roleplaying based note, the PCs have lost the opportunity to roleplay their reactions to that outcome as well. Some people may enjoy seeing how their character reacts to victory being at someone else's hands.
A more complex example might involve changing around an adventure based on the player ideas and excitement, and then claiming it was that way all along.
Well as long as it doesn't defy anything you've already told them, or it doesn't mean there's something you should have told them earlier and didn't, then that seems fine.
I mean, what's the difference between designing the adventure with player enjoyment in mind at 7pm the night before or at 4pm during the middle of the adventure?
So that doesn't bug me. I run all my games on the fly, so technically I'm constantly doing that.
The DM is in control of the rules, so from one point of view, he cannot cheat. Since you often have to lie to cover up a cheat and you aren't cheating, perhaps you aren't lying either.
I see the point. I don't agree with it, but I can see where you're coming from there and it does make sense.