The difficulty comes when prices of the two securities begin to drift apart, i.e. the spread begins to trend instead of reverting to the original mean.
Their marriage is initially a good one, but as the climate changes begin to impact on the surrounding environment, the couple start to cool towards each other and drift apart.
After a while, during their prison sentence, they all drift apart and have no intention of continuing from where they left off once they get out of jail. 15.
