There are two times in life that we surprise our family and not even know it.  First time is when we're born.  Second time is when you die.

Sure, mom and all the relatives know you're going to be born soon, but there is no exact time/day to predict when a baby is going to come into this world.  So, the day you pick to arrive is a surprise to everyone.

For the Senior Citizen, all the family knows you're going to die soon, but the same as with being born, there is no definite day to predict when you'll die. The day you die takes people by surprise.  "I just talked to him yesterday!"  "What do you mean he's dead??"