doctorbadwolf
Heretic of The Seventh Circle
No, the roll determines how well they perform. The DM determines how the environment reacts, often using that to set the DC, determine whether a check is needed or possible, and sometimes give advantage or disadvantage.Remember that the roll does not necessarily say how they are doing in general, but how the circumstances react to what they are doing. With the swinginess inherent to a d20 (compared to the bonusses), it would be absurd to consider that someone trained at stealth can be that good or bad just depending on what, their mood ?
The swing of the d20 exaggerates reality, but that can be mitigated, if you see it as a problem, by using fail forward and success with complication, as well as using the check to establish more interesting things that binarysuccess and failure, such as how expertly you navigate sneaking through the palace gardens, around guards, and up the side of the palace wall, to meet covertly with the princess.
no level of expertise ever means that you always perform at 100%. I’ve seen masters in thier field have to walk away from a task and come back after doing something else, when normally they’d be able to knock it out in minutes. Likewise, your master rogue may arrive at the meeting out of breath and disheveled, starting the meeting off on bad footing, frustrated, and out of sorts.