During this season’s first episode of TV’s “Dancing With the Stars,” actress Jennifer Grey surprised herself when she broke into tears upon hearing the song she and her partner would be dancing to. It was a song from the movie “Dirty Dancing,” which evoked strong memories of her friend and co-star Patrick Swayze, who died last year of complications from pancreatic cancer. Grey’s strong reaction, more than a year after her friend’s death, was normal. The song may have brought her back to a time when she and Swayze worked closely together on the film, allowing her to grieve the loss of her friend all over again.Almost everyone who’s lost someone they care for can describe a moment where a song, object or even a smell triggered a memory of the deceased and reignited feelings of loss and grief. As humans, our grief knows few boundaries. How well or long we knew the person cannot predict the intensity of our grief. We might grieve for someone we have known for a long time, such as a...