"Ain't No Mountain High Enough" is a promise with no escape clause. Marvin Gaye and Tammi Terrell recorded it in 1967 as a duet where both voices are making the same vow. No mountain. No valley. No river. No distance. The song lists every obstacle the physical world can put between two people and swears each one can be crossed. The hyperbole is the point. Love that does not sound a little extreme does not sound like love at all.