RPGMemes

Generally speaking it's considered bad practice for a GM to call for rolls that literally no one in the party can succeed at, but as with anything in tabletop roleplaying there is nuance.

There could be a narrative reason for the player to not know just how difficult something is and you don't want to give it away by just telling the players they can't succeed. If the most capable member of the party rolls a 20 and fails then the "reward" is the narrative of the attempt and learning what you're up against.

Or maybe someone in the party could succeed but for whatever reason the child-prodigy wizard with a strength of 8 wants to try lifting the portcullis. It wouldn't make any sense for them to actually do it.

I house rule it to anything where dumb luck might help anyway. deciphering a language you know nothing about? nah. lockpicking a simple lock despite not really having much of a skill? woah, you don't know wtf you did but things clicked. you could probably force it open with a high enough strength check too but hey.

If someone wants to jump into a cavern and use strength to flap his arms to fly, rolling a d20 can be to see how much the person fucked up. A 20 isn't an automatic success.

Same when someone mixes a potion, the d20 may be to see how much it will poison the creator if they drink it.

Roll to see how badly you fail.

the tension before DM can put on a self satisfied look and say "even that wasn't enough"

Generally speaking, to shut the player up about it

You could technically have negative modifiers that would make it impossible for you to succeed, where others might.

You're right in that your DM likely will not even let you roll....but it's still possible.