Some time ago on a far more interesting blog than this one there was some discussion about DM's rolling in public vs. fudging the dice, and while I don't really give a shit either way, one of the things that came out of this was the difference between primary dice rolls--like combat--and secondary rolls--like random encounters. To summarize, it was generally accepted that, while fudging primary rolls is verboten unless small children are involved, a little secondary fudge probably makes sense from time to time. Though there were, of course, some who felt that even this sort of leniency is a sure sign of the impending apocalypse.
Anyway, all this discussion reminded me of a situation that arose once back in my Old Time gaming days. My brother's ridiculously over-powered 10th level Cavalier was "clearing the lands" for his new stronghold and I was the DM for the event. I was 15 at the time and my brother was 18, I believe. I was halfheartedly rolling random encounters straight out of the DM's Guide and watching as my brother's cavalier ploughed through the Monster Manual like a hungry gamer through a plate of nachos.
It was a tedious affair and I really just wanted it to end when I rolled an encounter with a 9th level fighter. You might think "this could be a good fight" but this was shortly before Unearthed Arcana came out so only Cavaliers (the Dragon mag version) had weapon specializations. For those unfamiliar, this was a he-youuuuuu-ja advantage that allowed the cavalier something like 16 attacks per round at +32 to hit and damage with 9 different weapons at once. I exaggerate, of course, but I do remember that if my bother's cavalier was limited to inflicting a mere 20 points of damage in a single round it was considered a victory for the other side. Thirty to forty pts of damage were more the norm.
Anyway, I decided that this dude was clearing these very same lands for his own stronghold and thus a fight to the death was in order. So I rolled up a character and did some serious "secondary" fudging to determine his abilities and magic items. The result was a guy with 110 h.p., a vorpal sword, a +5 suit of platemail of etherealness, and a +3 shield. Even with his ridiculous hit points and armaments I knew this guy wouldn't last more than 4 rounds against my brother's munchkin-ass cavalier.
Ultimately, I was right. A few rounds into it the fighter pulled the rip cord on his armor and vacated the material plane. But not before staining my fingers in a fresh batch of rich and chocolaty primary fudge: on his first attack the unnamed fighter rolled a natural friggin' 20 with his vorpal sword. By all rights, the cavalier had just been handed his head, literally.
Now, my brother and I did not fight often and we generally got along pretty well. But I knew that if I let the chips fall where the dice said they had, the cavalier was not the only one who would be carrying his head around in a basket. Even if he didn't actually assault me physically I would have had to endure a Gestapo-like interrogation that I just didn't have the will to sustain. He would have questioned every decision and dice roll that led up to his headless horseman, and I am not to this day a very good liar in the heat of battle, so I would have folded and admitted that the vorpal blade was a fudger. I would have had to press reset, roll a new sword, and start all over. Except this time there would be a big, stinky cloud of resentment fogging the air around us. So I pretended it was a 19 and rolled normal damage.