Hurt is a gut punch
For me, it's Hurt. It was released in 2002. Every time I hear it I almost tear up... an aged Cash, his voice shaky, nearing the end of his time on earth, lamenting the things he did wrong. At my age, it's something that I can relate to.
The pain that he imbues the song with is so palpable that even Trent Reznor admitted that Cash "owns" the song now. His take is the definitive take that all others will be measured by.
Within a year or so, Cash would lose his wife. He would pass away just four months later.