For some unfathomable reason, there are no stairs where there should be.

因为某种不可理解的原因，该有楼梯的地方却没有。

《柯林斯英汉双解大词典》

He, for some unfathomable reason, wanted to be with me.

他因为某个不得而知的理由，想和我在一起。

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Indeed, even that video showed me an overlay banner ad for a local real estate company, for some unfathomable reason.

FORBES: Move up http://i.forbesimg.com t Move down

New York (CNN) -- This week I was sent on a three-day work trip to New York because, for some unfathomable reason, these people trust me outside the confines of my cube.

CNN: Apparently This Matters: Paging Dr. Mario