Cyberpunk 2020, the PnP RPG 2077 is based on, approaches Stealth like this: you say what you are going to do, "I sneak across to the forklift and hide behind it while the guards are talking." and then you roll your Stealth skill, plus any bonuses from gear, lack of light, rain, etc.
To detect you, the guards get an Awareness/Notice check, modified by their gear, if they are looking your way, level of paranoia, etc. Each guard and each observer system.
Thing is, in Cyberpunk, the visual range isn't like in videogames. If you can see them, they can see you. Yes, darkness helps, ( beaten by infrared/thermals), noise cover helps, (boosted audio, motion detector, sonar/radar built in) but the thing is, there isn't any "half-blind" NPCs a la Deus Ex or Dishonored.
Often, the enemy has Awareness/Notice really, really good, too. Because they are soldiers, cops or gang members in a violent world and they are dependent on it.
So you have to sneak into a facilty and pass every Stealth check, against detection gear, electronic systems, AIs and human patrols that are only going to be, in the Cyberpunk system, a few points worse at spotting you than you are at being hidden. Because, again, reality - the range of capability isn't superhuman typically.
As for disguise..in the real world or Cyberpunk...mercs know each other. So do cops. Gang members. Etc. You can try to bluff your way in, of course...
SO it's tough, really tough, to stay hidden that long. Try it sometime, sneaking around at night and not being seen by people whose job it is to spot you. Or sneaking up to within stab range. And you have to do this every time, whereas they only have to get lucky once.
It's thrilling, but it's tough.