If the GM is going to introduce complications that muck up the plans of, or thwart the desires of, players who make successful checks, then (from the player's point of view) what is the point of devoting resources to making successful checks?
Isn't that kind of the job of the DM? I mean, after they survive a combat, there's something else presenting a challenge, twist, or something, unless they've actually made it to their goal?
For example, let's say this scene isn't prewritten...
A PC is climbing a very high cliff, using pitons and rope. It's nearly impossible to be quiet, the hope is that there is nobody within earshot. He works his way up the cliff, mostly successful skill checks, an occasionally not-life-threatening failure (although they didn't know that at the time), and he reaches the top of the rocky cliff, that had a significant overhang, and is now working on climbing up the steep incline to a stone wall.
Just as he looks over the wall, a guard patrol is coming by and sees him. A fight immediately breaks out between our hero and the two guards. He manages to throw one of them off the side, but the other one successfully pushes him off. The rope holds, but he's hanging hundreds of feet above the ground, unable to reach the wall because of the overhang, so starts climbing back up the rope.
At the same time, the guard that didn't fall is hammering out the pitons. Causing our hero to fall a back a bit of the way he has climbed back up...
You know the rest.
He made successful skill checks, and successfully climbed the cliff, but didn't succeed in the goal of getting to the top undiscovered.
So there were a bunch of skill checks involved. They could have involved climb and stealth checks, with a passive perception, or active perception checks by the guards, etc. One option would have been that on one of the climb checks, it failed, but not by much.
Instead of having different stealth/perception checks, the DM decided that the hero was able to continue climbing, but the guard heard the hammering.
Why do it this way? Well, there are a lot of potential checks that could be made. A climb check when hammering in each piton, then a climb check to move the next 30' or so, and another for the next piton. In addition, checking against the passive perception each time a piton is hammered in, although there is no DC to check passive perception against, so it's either an active check, or the hero must roll a stealth check. He also may need to roll a stealth check while climbing to the next location where he'll hammer in a piton.
There are a lot of potential checks. Oh, yeah, and a bunch of fate checks to see if he pulls loose some rocks, or disturbs a nest full of birds, or a piton breaks free, or the rope gets snagged, etc.
So somewhere in here there is a sort of sweet spot where the right number and the right types of skill and event checks occur, combined with the right amount of narrative developed from the results of the skill checks.
Climbing several hundred feet 30' skill check at a time would get very, very long. But a single check isn't sufficient either.
A failed skill check could indicate he couldn't find a clear path to climb, a piton pulled loose, he drops a piton or the hammer, the rope gets snagged, the birds, loose rocks, etc. All of those seem to fit within the purview of the climb checks.
Some sort of perception check is needed by the guards. Probably the easiest is to use passive perception (they don't really think anybody is likely to be trying to climb up), and assign a penalty to the stealth checks for using a hammer. Or a flat DC can be set, saying anybody within 300 ft can hear it, up to 500' is a DC 12, 1000' is a DC 15, etc.
How many checks? That's the tricky one. That's where I like using the degrees of success/failure. If a moderate failure indicates an amount of time to recover, then a success over the amount needed can be used the same way. So, if the hero beats the DC by 7, then the next 7 rounds (210 feet) are traversed successfully, with little incident. A single stealth check covers the period, and continue on.
With fail forward, you can make some assumptions, and fill in the narrative blanks with fewer checks, and the end result of those checks potentially have a wider variety of results.
Now in this situation, I think what Pemerton is asking, is what if the hero made it all the way to the top, undetected, and a separate fate check indicated something very bad happened, and the slate of the final rock face came loose and slid off the clifftop, causing our hero to fall (and maybe the rope catches him). That just doesn't seem fair that he succeeded, and yet is still knocked back down.
The reality is that it's the same thing. In the end he's hanging by the rope and has to climb back up. Whether it's by design (the rock was designated as loose before he even climbed it), randomly (the fate roll declared it), a failed skill check (the DM picked the narrative based on the failed skill check), or because he failed against the perception of the guards and was knocked back off. The only real difference with the final one is that it would enter a combat phase and the PCs skills and design choices would come into play. But it's easy enough to add a Dexterity save when the rock starts sliding off.
The point is, any one of these mechanics will allow you to get to the same end result. But ultimately I think what is bugging Pemerton is that it removes the player's choices and the PCs actions from the equation, making it unfair. It's not unlike the save or die (or no save and die) of the AD&D 1st edition days. The sphere of annihilation trap in Tomb of Horrors is like that. No matter what you do, or how much time you put into your character development, they are suddenly gone, irrevocably, just because they decided to look into the dark hole.
Ilbranteloth