Death Comes in 3s

Sometime during the course of my life, I heard the expression "Death Comes in 3s."  I don't know if this "3" was supposed to be three strikes and you're out or if the three represented the Holy Trinity.  What I do know is that between two people in my life, there was a total of 3 deaths.  I thought there were only 2 deaths last week and was anticipating a third.  I learned yesterday the third had occurred and I was unaware.  I hope that completes the process this time and my friends can move on with their lives.  I don't think I can deal with any more talk of death.