No, it's an authentic observation from the pen of American icon Henry Wadsworth Longfellow. Longfellow conceived it 177 years ago. The year was 1841, and the 35-year-old poet wrote at his desk in Portland, Maine. The phrase is contained within the third stanza of Longfellow's “The Rainy Day.”

As Black Lagoon's Russian mobster implies, the saying means that misfortunes seem to come several at a time. The difference in the two sayings, then, is that "Into every life, a little rain must fall" is used in shrugging off a single misfortune, whereas "It never rains but it pours" notes a run of unhappy events.