How it could have been.
Could is a harsh word. Could is the nice word for "It, whatever you were wishing and hoping for, the same thing you've put all your effort and trust in, that thing which you would die for and commit your whole life to, didn't happen. So quit whining".
How many coulds in your life hinder you from the better things you ought to have?
Or more importantly, is that "could", whatever it is, be so important you're willing to give up what you already have.