Echoing a post I made in a thread the other day, I figured it would be worth it to clean up and post here.
The initial question was a good one:
DMs, do you fudge dice rolls? Why or why not?
It can be very tempting to save players from themselves, but in the long run I think it hurts the overall dynamic of the game. I read once that a good GM should be a like a coach on a sports team. They are there to help advise, encourage, support, and cheer for the players as best they can, but it's still up to them to play the game.
OSR can be brutal in a lot of ways. One of the tropes people tend to attribute to OSR play in particular is the high lethality. For some people, the Fantasy Vietnam thing is actually part of the draw. Even when you're not intentionally aiming for that style, things happen. Old-school play has a lot of save-vs-terrible things moments. The level 1 "wandering encounters" table for B/x has a whole bunch of results that could easily TPK a group. Because OSR has so much randomness and so much of it can be absolute murder, it's very important that the players and the GM are on the same page. The GM should be seen as an impartial arbiter of these results, rather than the cause of them. You need the culture at the table to be "that's just what the dice said."
Once you start fudging dice and the players know that this is a precedent, the GM is now culpable for every result the dice show. At best, whenever something bad happens to a player's character, they know you could have prevented it. When a character dies, it's because you let them die. "But we fudged the roll last time!"
More insidious than this though can be the rolls they don't see at all. The villainous NPC making a difficult or important saving throw, or landing a critical blow in combat can be seen as you cheating to save your BBEG. A bad wandering encounter result or similar random-chart-result situation could simply be seen as you trying to screw the players. Even if you know you aren't trying to, and the players know you aren't trying to, it can still look terrible.
For me at least, it's way better for it to be firmly established that the dice have the final say and that I'm not going to fudge things one way or another. I do this for the same reason I want a GM looking when I roll ability scores for a character. Sometimes crazy results occur, and I don't want someone going "yeah, I'm sure you totally rolled two 18s."
Up until now, I've spoken almost exclusively about OSR style games, but I think the same principle applies in more story-oriented games as well. You want the results to appear impartial.The counter is often something along the lines of "I don't want a single bad roll to derail the story," but fortunately story-based games make this even easier than OSR games do. If it's not something you're willing to risk the PCs failing don't ask them to make a roll. Narrative games are pretty great that way.