[4][5] Based on the true story of Bae Hyeong-jin [ko], an autistic marathon runner,[6][7] the film popularized the South Korean term for autism (자폐증; japyejeung) which can be translated as "self-closed syndrome.

As a child, Cho-won regularly had meltdowns, bit himself, and struggled to communicate with others—finding solace only in zebras and the Korean snack, choco pie.

Even though their family suffers from financial difficulties, they find a former marathon champion, Jung-wook — now a lethargic older man with an alcohol problem.

Jung-wook, who is serving community service hours as a physical education teacher for a DUI, grudgingly accepts the offer to train Cho-won in marathon running, but eventually becomes lazy with him.

The movie shows the emotional struggles of a mother who is not sure if she is forcing her son to run or if it truly is his passion.