Probably the most frequent comment couples may be heard to make about marriage is that 'it has its ups and downs.' The ups are the time when love is plain as day, big as life and fully visible (visible, that is, to the conscious mind and the feelings). But the downs are the times when love goes undercover, incommunicado, so that there may appear to be nothing left of it at all. So commonplace is this observation about the 'ups and downs' of marriage that one wonders whether it shouldn't be written right into the vows. But of course, it is: 'for better, for worse...'
--taken from "The Mystery of Marriage" by Mike Mason