It depends on the size of the opening. If it's small that's no problem. You could block a 1 inch pipe at 10psi with your bare hand and be largely fine. It's a little less than 10 pounds of force assuming a round opening.
The problem is that the total force scales geometrically with the size of the opening. Make it two feet wide at the same 10psi and now you've got about 4500 pounds of force trying to push you though that opening should you find yourself in the unfortunate situation that it's been completely blocked by your body.
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.