Ross Gay set himself one rule — write a short essay about a delight every day for a year, starting on his 42nd birthday — and got a book of “essayettes,” some a paragraph, some five pages. Loquats picked off a tree in Italy he had wrongly assumed was public. A teenager in a Def Leppard shirt high-fiving him at work. What he reports back is that the practice grew a “delight radar,” and that it never once required pretending the sorrow wasn’t there.