Three days? Three months? Three years?
Or three lifetimes?
For most of us, it's the latter. That's just what love does.
Conventional wisdom says otherwise - that after a short period of time, a missing person is most likely to stay missing. And often, the worst is presumed.
But sometimes, love is right. Sometimes, love trumps logic.
Shawn Hornbeck's mother and stepfather never gave up, even after four years since his Oct. 6, 2002 disappearance while riding a bike in a St. Louis suburb.
Common sense might have told them he would never come back. They listened to their hearts instead - ultimately quitting their jobs, spending all their money and going into debt in an effort to find him. They started a Shawn Hornbeck Foundation to help others in their situation.
They turned a tragedy into a triumph, with sheer force of will, hope, faith, hard work and, no doubt, more than a little providence.
Most of all, they didn't give up.
Again, it's against the odds to expect such a result. But every now and then we get a reminder of the need to hope. Elizabeth Smart of Utah was rescued after nine months in captivity. Austrian Natascha Kampusch escaped a captor after eight years. Elke Hoerscher found her daughter Angeline after five years and 11 million postcards and fliers.
People sometimes reappear even after the search has ended. South Carolinian Carolyn Dorn, 52, was recently discovered in the Gila National Forest in New Mexico five weeks after she got trapped by a swollen river - and two weeks after they gave up looking.
"You don't give up," said Det. Tom Watley of Delray Beach, Fla., who helped find Angeline. "You can never give up."
"It's a miracle she came out alive," a searcher said of Dorn.
Ah, but miracles happen.
Some of them you read about in the Bible.
Others you read about in your morning newspaper.