There is titillating pleasure in looking back at the past and asking oneself, 'What would have happened if...' and substituting one chance occurrence for another, , observing how, from a gray, barren, humdrum moment in one's life, there grows forth a marvelous rosy even that in reality had failed to flower. A mysterious thing, this branching structure of life: one senses in every past instant a parting of ways, a 'thus' and an 'otherwise', with innumerable dazzling zigzags bifurcating and trifurcating against the dark background of the past.