Found what looks like a v interesting blog:
I have a theory. My theory is that the parting is contained in the greeting. Is this a theory? No, it is an observation. My observation is that one knows from the beginning why a relationship will fail, that the problem is plain and yet one pretends not to see it; or perhaps one admits to seeing it but downplays its significance. The flush of love, or attraction, or simply of hope, is a powerful hallucinogen, one that causes us to see things that are not there and to fail to see things that are. A relationship does not begin in earnest until the effects of this drug have worn off.