One of the most obvious laws on this planet is the passage of time in one single direction. Or at least this is how we perceive it. We may write books, make movies and fantasize about reversing time, but I have not met anyone yet who has done this, have you? So when something undesirable happens, it just cannot be undone, it is forever recorded in the archives of history which makes dwelling on it kind of pointless. It is the now and the future that we can influence, the past is only there to learn from.