JonnyP71
Explorer
Rolls can be failed. If there was a shiny sword that upon closer inspection is clearly glowing and magical, I'd just tell the player that his PC sees that it is magical when his PC investigates the sword. However, if that player instead of telling me that he is investigating the shiny sword instead says, "I investigate the sword and make an arcana check to see if it is magical. (a die gets rolled)". At that point he has now introduced a roll that can be failed as rolls in 5e happen when the outcome is in doubt. Should he roll a 1 and end up with a really low number, he has probably failed. As soon as he rolls I need to assign a DC to that check. It would be an easy one, but even easy checks can fail. On a failed check I would let him know that the sun is reflecting brightly off of the blade, or some other reason why the PC would miss the glow.
As you say, rolls are a measure of performance and performances can go wrong.
Some players will hate my approach, but I've done similar in the past. If a player keeps rolling before being asked to, despite already being asked to wait, then yes, I might introduce low DC, even if I would otherwise have given them an auto-success.
The player, by ignoring a simple request, has created the chance of failure.
However the reverse does not apply. If they roll before being asked and get a 20, and I deemed the task to be impossible, then they still fail.
...therefore a net loss for the player.