I should have worded that as "clearly this door is an impassable false door", because our point is that it's not like the player abandons all interest in seeing what's through the door. If I fail at Pick Lock, I know that the PC couldn't do it under those specific circumstances. Maybe with a bit of luck or whatever in-game condition the check abstracts, they could have. There's still something I want to address, so I ask the fighter to bust down the door or get out my stone to mud wand or whatever. I don't necessarily abandon it.
Now apply the same logic to Sense Motive. To treat social/knowledge skills differently, to assume by definition now the character is compelled to give up, is the folly we're invoking.