Sometimes, a song takes on a life of its own.

Sara Bareilles says that when she wrote “She Used to Be Mine,” the 11 o’clock number from her Broadway musical “Waitress,” it seemed so insanely specific (“she is all of this mixed up and baked in a beautiful pie”) that she felt self-conscious performing it in concert.

But audiences have a way of making decisions for themselves. The song, written for a pregnant, abused waitress, reflecting back on the dreams she did not achieve, has been claimed, unexpectedly, by men, by children, by singers of all sorts.

“The range of who this song speaks to is much broader than I could have anticipated,” Ms. Bareilles said. “The chasm between who we are, and who we thought we would be, is always something we’re negotiating.”

Covers of the song caught my attention when a video of a gut-punching version by a 14-year-old boy from western Pennsylvania went viral in the fall. Then I started to notice it popping up on set lists. Heather Headley, a Tony winner for “Aida,” put her version on a new album alongside standards like “Over the Rainbow.” Just last week, Kathryn Gallagher, an actress in the cast of the Broadway-bound “Jagged Little Pill,” performed her own take, accompanied by a cello, at a Midtown bar, encouraged to do so, she said, by fans online.