It has been more than a week since Malaysia Airlines Flight 370 disappeared, and despite a massive search effort, the whereabouts of the plane and the 239 people on board are unknown.
The airline has told the families and friends of those missing to "expect the worst."
But it's tough for families to grieve without knowing the answer to a crucial question: Could my loved one still be alive?
Dr. Pauline Boss works with people in this kind of situation. She's the author of "Loss, Trauma and Resilience" and a professor emeritus at the University of Minnesota.
She says the families and friends of the missing are experiencing an "ambiguous loss."
"[It's] the most painful kind of loss there is right now, because you have no assurance of the fate of your loved one," she says.
People suffering with this kind of loss often blame themselves, says Boss. A large part of her job is to remind them that the situation is not their fault. But even as a grief counselor, Boss says there is a limited amount she can do to help. Grieving — and healing — simply take time.
"They aren't going to move forward right now. Right now they're in a survival mode," she says. "The only way I've found that families of the missing move forward is if you allow them to hold the paradox that ambiguity causes.
"At one moment they'll say, 'I think they're at the bottom of the sea.' At another moment they'll say, 'I think perhaps they're alive on an island somewhere.' That is normal. That is natural and typical reactions from ambiguous loss."
Sometimes the ambiguity surrounding the loss persists for a lifetime, or even across generations, says Boss. How one deals with that ambiguity depends in part on culture.
"The problem is that those from very can-do cultures, from very mastery-oriented cultures, are used to having answers to all problems. And this is a case where you'll never have an answer," she says. "If that is the case, that you never have an answer, the only option left is to learn to live with the ambiguity."
Embracing that can be painful, says Boss, but it is ultimately a good thing for those suffering loss.
"They become more resilient and stronger for it. They are aware now that life will not always go their way," she says.
Even if people can personally accept not knowing the fate of their loved ones, they can still experience the social isolation that often comes with the grieving process.
"Society is really rough on the families of the missing. They don't understand quite what to do, and unfortunately what people tend to do therefore is stay away," Boss says. "Please don't stay away from these families. But there isn't much you have to say to them. Your presence will be support enough in many cases."