La La Land (2016)

La La Land's ending devastates because it dares to show love as a casualty of ambition—Mia and Sebastian share a silent, tear-soaked smile that dissolves romance into reality. Chazelle's dream montage, which cost $2.3 million to film, reimagines their alternate life with wrenching visual detail. This bittersweet finale polarized audiences: 62% of Movieline readers in 2017 voted it the most heartbreaking ending of the decade, yet it also sparked intense debate about whether professional success is worth the cost—a question #9 Grease (1978) avoids entirely by defaulting to fantasy.