One unfortunate truth about human beings is our general inability to know ourselves adequately. Most people, I'd harzard, would imagine themselves to be reasonably egalitarian but, in reality, have hidden laundry-lists of must-have attributes. Now, they may not secure a mate who has most (or any) of these hidden attributes, but they will simply then resent their mate silently, perhaps for decades.

People who are self-aware to a larger degree, and who have achieved hard things, tend to avoid less developed individuals and so have far fewer options - but options of a more satisfying quality.