Conundrums of idiomatic usage

"Romance is in the air."

Ah, yes. Lovely image. But where is romance when it is not in the air? Can it be, for example, on the ground? Or in the trees? I rather think not. Indeed, in all my years of linguistic observation, I've never heard tell of it being anywhere but in the air. Yet I find it impossible to explain why.

"She marched out of the room in high dudgeon."

We get the picture. She was seriously annoyed. But is high dudgeon really a question of degree? It can't be; otherwise, it would be possible to stomp out in low dudgeon, just a little annoyed, and it isn't.

Idiomatic expressions have to be taken on faith. Those of us who know the idioms form the appropriate pictures. Unfortunately for language learners, those who don't know may not even be aware that they are missing the idea.

After all, if she left the building in high dudgeon, couldn't that be a vehicle? Or a high-collared coat? In that case, though, we would need an article in front of high dudgeon: a high dugeon. Native speakers know that an article is never used with dudgeon, but English article usage is so idiomatic that most second language speakers would be unlikely to notice that it wasn't there.