A year after his only daughter died at age 38 of an asymptomatic heart condition, Roger Rosenblatt wrote an essay in The New Yorker titled, “Making Toast.” He describes how he and his wife moved into Amy’s house in Bethesda, Md., to help their son-in-law care for the couple’s three small children, and how the myriad, mundane activities of child-rearing provided a measure of solace for his inconsolable grief. His latest book, “Kayak Morning: Reflections on Love, Grief, and Small Boats,” was written after the essay was turned into a best-selling book. What he has discovered in the more than 2 1/2 years since her death is that just getting on with life — captured in the closing image of the essay when his 23-month-old grandson asks for toast — hasn’t worked. “What I failed to calculate is the pain that increases even as one gets on with it,” he writes.