-- Rachel Platten's hit "Fight Song" might be one of the biggest inspirational anthems of 2015, but the singer says she didn’t mean for anyone else to hear it at first — and she wasn’t sure if anybody ever would.
"Ten months ago I was on a house concert tour in a van playing to like twenty or thirty people a night," Platten said in an interview for the ABC News special "The Year: 2015" hosted by ABC News' Robin Roberts. "I wrote the song when I was going through such a hard time and I needed to remember to believe in myself. ... So the fact that it's reached anyone other than me is really incredible."
Platten said she spent nearly a decade trying to make a successful music career for herself, carrying her own keyboard and playing cover gigs and performances from 1 a.m. to 4 a.m., in New York City.
"When I wrote 'Fight Song,' I was in a particular low point. I needed to remind myself to not give up, that I still believed in myself and that I still had fight left," Platten said. "I didn't intend to write ['Fight Song'], you know, for the world to hear to be honest. I wrote it 'cause I needed it. And I wrote it 'cause I needed that reminder and I needed hope. And maybe there was this tiny place in my heart that I believed this could still happen. And the fact that it did is crazy."
Within 72 hours of hearing her song on the radio for the first time, Platten said she was signed to a major label.
"I don't know if that hit me truly until ... gosh ... I don't know, maybe on tour this summer when I started to finally see audiences sing those words back to me," Platten said. "And I got to do it all because of this song that I wrote when I was in one of the darkest places in my life."
Platten's debut album, "Wildfire," comes out on Jan. 1, and she will soon be going out on her first headlining tour. But she's still getting used to her success.
"I am so grateful for all of it. It really blows my mind," Platten said. "My life has changed so drastically this year. And every, every single dream that I ever imagined has come true."
Watch "The Year: 2015" hosted by ABC News' Robin Roberts HERE.