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.