I apologize for not having a reference, but I remember reading a study that looked at different types of painful events, and found there are 2 main events that

I apologize for not having a reference, but I remember reading a study that looked at different types of painful events, and found there are 2 main events that have a pretty much permanent effect on happiness levels: death of a child and death of a spouse. Yes, the acute grief fades, but the sense of loss (the void as Ms. Sandberg puts it) never really goes away.