That sounds like a partial success, but if it doesn’t sound like one to the player, you can always pause the game to talk about why! The rulebook also touches on how the referee and players can avoid creating this dissonance in the first place – ask if you’re giving them enough information to make good decisions; prompt them to give you details about how they’re trying to do something; experiment with telling players upfront what will happen if they roll a partial or failure on an action they’re considering. As referee, you’re acting as the game environment, so you’re supposed to surprise the player but also telegraph what to expect to a degree that allows them to account for it if they try. Both player and referee must be able to accurately extrapolate and strategize around likely risks. Here’s an imagined run of your scenario, with plenty of material to play off of provided by both parties:
REF: “So, you’re heading toward the ladder. It’s old, a little warped. You can see the guard still trying to scrape the gum off their boot, but they’re probably not super invested in that, so you’ll have to be quiet… how are you doing this?”
PLAYER: “I’m gonna slip off my shoes and string them around my neck so I don’t make noise on the rungs.”
REF: “Okay, roll TACTICAL…”
PLAYER: “I got a 7.”
REF: “You make it up the ladder without a sound – until the very last rung. As you heave yourself onto the roof, it snaps and clatters one thunk at a time down the ladder. Gumshoe down there staggers out of flamingo stance and glances around, and at the same time you realize you’re not alone up here – there are footsteps approaching, but not with any urgency. There are no shadows on hand to duck into. What’s your move?”
If the players are properly prepped for the pulp action tone, this should feel like the next exciting catalytic beat. A good action movie is rarely one where the hero is never noticed and gets home half an hour early. If anyone is having trouble getting in the groove of FIST, we suggest watching any movie (or video game, or whatever) you can map to its mechanics, which is how the game was created and is the main point of it. Here’s a clear example of a sequence of partial successes: Garth Marenghi's Gun Possession
If the player is dissatisfied with the results of a bad roll, they may not realize the game won’t happen if no bad rolls do because bad rolls give the environment opportunities to progress and interact with the players’ agency. It might be helpful to go over these parts of the book with the whole table to get you all on the same page and in the right frame of mind:
p.5 Rolling the dice
p.7 Playing dirty
p.16 Playing fair
p.17 Quality fiction
p.19 Using agency
p.21 Referee FAQ
These sections go over stuff like preparing for and embracing the consequences of bad rolls as the dramatic meat of the game, how you can use creative thinking and strategy to tip stacked odds to your favor, what the table should mutually agree on, and general referee tips. There's also a spark table for partial successes on page 148.
Hope this helps and isn’t too much of a wall!