DM: "You see a wooden door"
P: "I check the door for traps, and if there is none, I open the door"
DM: "Ok, it appears clear of traps, and the door swings open smoothly"
P: "Ok, I step through"
DM: "You bang your head on the door, as the door is closed."
P:"Wait... what? I just opened it"
DM: "You did. But the door is closed"