"You can't un-think a thought, either it's there or its not." This line totally sets the stage for the rest of the song. There's something wrong and she isn't sure if she should voice the problem or not. Basically she's getting seriously involved with someone and is unsure if it's what she wants. The mountain is the relationship and the thing that is under it is some kind of secret or problem that is making her doubt getting involved with whoever she is singing to. The mountaineers, believing they would know what to do, try to climb the mountain, or in other words the relationship, but there's still the underlying uncertainty. When the song is reaching its climax basically she is asking "should we do this, should we ignore the problem to continue this relationship even though there's always going to be something hiding just under the surface?"
"You can't un-think a thought, either it's there or its not." This line totally sets the stage for the rest of the song. There's something wrong and she isn't sure if she should voice the problem or not. Basically she's getting seriously involved with someone and is unsure if it's what she wants. The mountain is the relationship and the thing that is under it is some kind of secret or problem that is making her doubt getting involved with whoever she is singing to. The mountaineers, believing they would know what to do, try to climb the mountain, or in other words the relationship, but there's still the underlying uncertainty. When the song is reaching its climax basically she is asking "should we do this, should we ignore the problem to continue this relationship even though there's always going to be something hiding just under the surface?"