There is never a right time to break someone's heart. And anyone with even a microgram of sensitivity in his or her body will agonise for an age over that timing. Only problem is there is always some reason not to make someone unhappy. The day a relationship end, if that relationship was at all important to the suckers involved, becomes as important an anniversary as a wedding day or birthday.
Obviously, the average person doesn't want to kick someone they once loved while that person is down.
It's not just hard times when someone is down that become obstacles to making your getaway. After times of bereavement, unemployment and general unhappiness, those events that should be happy ones also make some times off limits for the eager would- be dumper. Christmas, birthdays, Easter all impossible. A clever person with a sensitive lover that they sense is not quite as into them as he or she used to be, could starve off the inevitable for years by carefully spacing out this crucial dates.