Those of us who live long lives are generally considered lucky. But such people are also unlucky in the sense that they suffer the loss of loved ones and grieve in their absence.
The most popular notion about grief comes from Swiss-born psychiatrist Elisabeth Kubler-Ross.
She described five stages of loss, progressing from denial, anger, bargaining, depression to acceptance. However, her work was based on terminally ill patients in a Chicago hospital and not on people who were grieving.
More recent research by Dr George Bonanno from Columbia University revealed that grief can take many different journeys. He also found that most of us come out of it reasonably well.
As he wrote in his book, The Other Side Of Sadness: "As frightening as the pain of loss can be, most of us are resilient. Some of us cope so effectively, in fact, we hardly seem to miss a beat in our day-to-day lives. We may be shocked, even wounded by a loss, but we still manage to regain our equilibrium and move on.
"That there is anguish and sadness during bereavement cannot be denied. But there is much more. Above all, it is a human experience. It is something we are wired for, it is certainly not meant to overwhelm us. Rather, our reactions to grief seem designed to help us accept and accommodate losses relatively quickly so that we can continue to live productive lives".
But there is another sort of grief that is more extraordinary and far more complicated. Indeed, the world has seen it played out almost daily for the past few weeks on television as well as in print and social media. In particular, the world has watched with a strange mixture of pity, compassion, and more latterly, bafflement, impatience and even anger.
To many, the reaction of the relatives of the 153 Chinese passengers on MH370 seems excessive, unreasonable and even atavistic.
But there is another way of looking at this. The behaviour of the relatives is not abnormal. What is abnormal is the situation that they have so suddenly found themselves in, and the fact that they have to continue living through it without any end in sight.
For the relatives of the passengers and crew of MH370, as long as the ongoing search effort turns up nothing, they will continue to have what Professor Pauline Boss, professor emeritus at the University of Minnesota, calls "ambiguous loss".
This refers to a situation in which a family member is physically missing, but psychologically present because it is unclear whether that person is dead or alive.
This, in Prof Boss' view, is the most stressful loss people can face. Prof Boss, who is the author of the classic study, Ambiguous Loss: Learning To Live With Unresolved Grief, notes that it is unlike a well-defined and certain death.
In the case of the latter, mourning can start and bring with it all the attendant rituals and support culminating in a funeral. But with MH370, there is, as yet, no official verification, no definitive proof of death, and hence, no possibility of closure or finality.
In consequence, the relatives in the throes of this ambiguous loss can seem resistant to reasoning, implacable and even dysfunctional.
They are likely to experience a maelstrom of emotions: anxiety, regret ("what ifs"), guilt, depression, and utter helplessness.
And all this is leavened occasionally with some glimmer of hope before the plunge back into despair.
Without reliable information to clarify their loss, without irrefutable evidence of death, they have to cope with the "paradox of absence and presence". They can't even start the normal process of grieving. In the words of Prof Boss, "the grief process is frozen and so is the coping process".